Citation Nr: 0616316 Decision Date: 06/05/06 Archive Date: 06/13/06 DOCKET NO. 98-00 703 ) DATE ) ) On appeal from the Department of Veterans Affairs Regional Office in San Diego, California THE ISSUE Entitlement to service connection for colon cancer, including claimed as secondary to asbestos, chemical and ionizing radiation exposure. REPRESENTATION Veteran represented by: Disabled American Veterans ATTORNEY FOR THE BOARD K. Morgan, Associate Counsel INTRODUCTION This case comes before the Board of Veterans' Appeals (the Board) on appeal from an October 1996 rating decision of the Department of Veterans Affairs (VA) Regional Office in San Diego, California (the RO). Procedural History The veteran served on active duty from December 1953 until December 1983. In May 1996, the RO received the veteran's claim of entitlement to service connection for colon cancer. The October 1996 rating decision denied the veteran's claim. The veteran disagreed with the October 1996 rating decision and initiated this appeal. The appeal was perfected by the timely submission of the veteran's substantive appeal (VA Form 9) in January 1998. This matter was previously before the Board in March 2000. At that time, the veteran's claim was remanded for additional development concerning claimed in-service occupational radiation exposure as a source of the colon cancer. The development specified in that remand has been completed, and the RO issued Supplemental Statements of the Case (SSOC) in December 2002 and October 2004 which continued to deny the veteran's claim. In February 2005, the Board determined that a defect in notice required under the Veterans Claims Assistance Act of 2000 (VCAA) necessitated an additional remand. See Disabled American Veterans, et. al. v. Secretary of Department of Veterans Affairs, 327 F.3d 1339 (Fed. Cir. 2003) [A procedural defect with respect to notice required under the VCAA may not be cured by the Board]. The development required by the Board's February 2005 remand has been completed. In November 2005, the Agency of Original Jurisdiction (AOJ) issued a SSOC which continued to deny the veteran's claim. This case has again been returned to the Board for further appellate action. FINDING OF FACT A preponderance of the medical evidence of record demonstrates that the veteran's colon cancer is not etiologically related to any incident of service, including exposure to asbestos, chemicals or ionizing radiation. CONCLUSION OF LAW The veteran's colon cancer was not incurred in or aggravated by service, nor may it be presumed to have been incurred therein. 38 U.S.C.A. §§ 1110, 1112, 1113, 1131, 1137 (West 2002); 38 C.F.R. §§ 3.303, 3.307, 3.309, 3.311 (2005). REASONS AND BASES FOR FINDING AND CONCLUSION The veteran is seeking entitlement to service connection for colon cancer. He contends that alleged in-service exposure to chemicals, asbestos or radiation caused him to develop colon cancer after service. Alternatively, he contends that in-service bowel symptomatology establishes chronicity for his post- service colon cancer and that service connection should be granted on that basis. In the interest of clarity, the Board will initially discuss certain preliminary matters. The Board will then address the pertinent law and regulations and their application to the facts and evidence. The Veterans Claims Assistance Act of 2000 The Board has given consideration to the VCAA, which includes an enhanced duty on the part of VA to notify a claimant as to the information and evidence necessary to substantiate claims for VA benefits. The VCAA also redefines the obligations of VA with respect to its statutory duty to assist claimants in the development of their claims. See 38 U.S.C.A. §§ 5103, 5103A (West 2002). The Board has carefully considered the provisions of the VCAA and the implementing regulations in light of the record on appeal, and for reasons expressed immediately below finds that the development of the issue has proceeded in accordance with the provisions of the law and regulations. Notice The VCAA requires VA to notify the claimant and the claimant's representative, if any, of any information and any medical or lay evidence not previously provided to VA that is necessary to substantiate the claim. As part of the notice, VA is to specifically inform the claimant and the claimant's representative, if any, of which portion, if any, of the evidence is to be provided by the claimant and which part, if any, VA will attempt to obtain on behalf of the claimant. See 38 U.S.C.A. § 5103 (West 2002); see also Quartuccio v. Principi, 16 Vet. App. 183 (2002) [a letter from VA to an appellant describing evidence potentially helpful to the appellant but not mentioning who is responsible for obtaining such evidence did not meet the standard erected by the VCAA]. After having carefully reviewed the record, the Board has concluded that the notice requirements of the VCAA have been satisfied with respect to the issues on appeal. The Board observes that the veteran was informed of the relevant law and regulations pertaining to his claim in the November 2005 SSOC. Specifically, the SSOC detailed the evidentiary requirements for service connection. Crucially, as directed in the Board's February 2005 Remand, the AOJ informed the veteran of VA's duty to assist him in the development of his claim in a letter dated March 29, 2005. This letter advised the veteran of the provisions relating to the VCAA. Specifically, the veteran was advised in this letter that VA would obtain all evidence kept by the VA and any other Federal agency, including VA facilities and service medical records. He was also informed that VA would, on his behalf, make reasonable efforts to obtain relevant private medical records not held by a Federal agency as long as he completed a release form for such. The letter specifically informed the veteran that for records he wished for VA to obtain on his behalf he must provide enough information about the records so that VA can request them from the person or agency that has them. Finally, the Board notes that the letter specifically notified the veteran that he could submit or describe any additional evidence that may be relevant to his claim. The requests contained within that letter comply with the "give us everything you've got" requirements of 38 C.F.R. § 3.159 (b) in that the veteran was informed that he could submit or identify evidence other than what was specifically requested by the RO. In short, the record indicates that the veteran received appropriate notice under 38 U.S.C.A. § 5103 and Quartuccio. Recently, in Dingess v. Nicholson, No. 01-1917 (U.S. Vet. App. March 3, 2006), the United States Court of Appeals for Veterans Claims (the Court) observed that a claim of entitlement to service connection consists of five elements: (1) veteran status; (2) existence of a disability; (3) a connection between the veteran's service and the disability; (4) degree of disability; and (5) effective date. The veteran in this case seeks to entitlement to service connection. Because a service connection claim is comprised of five elements, the Court further held that the notice requirements of section 5103(a) apply generally to all five elements of that claim. Therefore, upon receipt of an application for a service connection claim, section 5103(a) and section 3.159(b) require VA to review the information and the evidence presented with the claim and to provide the claimant with notice of what information and evidence not previously provided, if any, will assist in substantiating or is necessary to substantiate the elements of the claim as reasonably contemplated by the application. This includes notice that a disability rating and an effective date for the award of benefits will be assigned if service connection is awarded. In this case, element (1), veteran status, is not at issue. Moreover, elements (4) and (5), degree of disability and effective date, are rendered moot via the RO's denial of the veteran's claim of entitlement to service connection. In other words, any lack advisement as to those two elements is meaningless, because a disability rating and effective date were not assigned. Element (2), existence of disability, is conceded. The veteran's claim of entitlement to service connection was denied based on a lack of evidence as to element (3), relationship of such disability to the veteran's service. As explained above, he has received proper VCAA notice as to his obligations, and those of VA, with respect to that crucial element. Thus, there is no prejudice to the veteran in Board's considering this case on its merits. See Soyini v. Derwinski, 1 Vet. App. 540, 546 (1991) [strict adherence to requirements in the law does not dictate an unquestioning, blind adherence in the face of overwhelming evidence in support of the result in a particular case; such adherence would result in unnecessarily imposing additional burdens on VA with no benefit flowing to the veteran]. The veteran is obviously aware of what is required of him and of VA. Indeed, he has personally submitted evidence and argument in support of his claim, the tenor of which leads the Board to conclude that he is well informed and aware of his obligations. Because there is no indication that there exists any evidence which could be obtained which would have an effect on the outcome of this case, no further VCAA notice is necessary. See Dela Cruz v. Principi, 15 Vet. App. 143, 149 (2001) [VCAA notice not required where there is no reasonable possibility that additional development will aid the veteran]. Duty to assist In general, the VCAA provides that VA shall make reasonable efforts to assist a claimant in obtaining evidence necessary to substantiate claims for VA benefits, unless no reasonable possibility exists that such assistance would aid in substantiating the claim. The law provides that the assistance provided by VA shall include providing a medical examination or obtaining a medical opinion when such an examination or opinion is necessary to make a decision on the claim. An examination is deemed "necessary" if the record does not contain sufficient medical evidence for VA to make a decision on the claim. See 38 U.S.C.A. § 5103A (West 2002); 38 C.F.R. § 3.159 (2005). The Board finds that reasonable efforts have been made to assist the veteran in obtaining evidence necessary to substantiate his claim, and that there is no reasonable possibility that further assistance would aid in substantiating it. In particular, the RO has obtained the veteran's service medical records, a radiation dose estimate and treatment records. The Board notes that although the AOJ requested records from Dr. L.J.M., the doctor's office responded that these records were unavailable. The veteran has identified no additional information or evidence that should be obtained. The duty to assist also includes providing a medical examination or obtaining a medical opinion when such an examination or opinion is necessary to make a decision on the claim. 38 U.S.C.A. § 5103A(d) (West 2002); 38 C.F.R. § 3.159(c)(4) (2005). To that end, appropriate medical opinions were obtained in March 2002 and July 2004. Accordingly, the Board finds that under the circumstances of this case, the VA has satisfied the notification and duty to assist provisions of the law and that no further actions pursuant to the VCAA need be undertaken on the veteran's behalf. The Board additionally observes that all appropriate due process concerns have been satisfied. See 38 C.F.R. § 3.103 (2005). The veteran and his representative have been accorded the opportunity to present evidence and argument in support of this claim. The veteran originally requested a hearing but subsequently withdrew that request. Pertinent Law and Regulations Service connection - in general Service connection may be granted for disability resulting from disease or injury incurred in or aggravated by active service. 38 U.S.C.A. §§ 1110, 1131 (West 2002); 38 C.F.R. § 3.303 (2005). Service connection may also be granted on a presumptive basis for certain chronic disabilities, including malignant tumors, when manifested to a compensable degree within the initial post-service year. See 38 U.S.C.A. §§ 1101, 1110, 1112, 1113, 1131, 1137 (West 2002); 38 C.F.R. §§ 3.307, 3.309(a) (2005). In order to establish service connection for a claimed disorder, there must be (1) medical evidence of a current disability; (2) medical, or in certain circumstances, lay evidence of in-service incurrence or aggravation of a disease or injury; and (3) medical evidence of a nexus between the claimed in-service disease or injury and the current disability. See Hickson v. West, 12 Vet. App. 247, 253 (1999). Service connection - asbestos exposure There is no specific statutory guidance with regard to asbestos-related claims, nor has the Secretary of VA promulgated any regulations in regard to such claims. However, VA has issued a circular on asbestos-related diseases. DVB Circular 21-88-8, Asbestos-Related Diseases (May 11, 1988) provides guidelines for considering compensation claims based on exposure to asbestos. The information and instructions from the DVB Circular have been included in a VA Adjudication Procedure Manual, M21-1 (M21- 1), Part VI, 7.21. VA Manual M21-1, Part VI, para. 7.21 (October 3, 1997) provides that inhalation of asbestos fibers can produce fibrosis and tumor, most commonly interstitial pulmonary fibrosis (asbestosis). Asbestos fibers may also produce pleural effusion and fibrosis, pleural plaques, mesotheliomas of pleura and peritoneum, lung cancer, and cancers of the gastrointestinal tract. Cancers of the larynx and pharynx, as well as the urogenital system (except the prostate) are also associated with asbestos exposure. Thus persons with asbestos exposure have increased incidence of bronchial, lung, pharyngolaryngeal, gastrointestinal and urogenital cancer. M21-1, Part VI, para 7.21(a). The applicable section of Manual M21-1 also notes that some of the major occupations involving exposure to asbestos include mining, milling, work in shipyards, carpentry and construction, manufacture and servicing of friction products such as clutch facings and brake linings, manufacture and installation of roofing and flooring materials, asbestos cement and pipe products, military equipment, etc. High exposure to respirable asbestos and a high prevalence of disease have been noted in insulation and shipyard workers, and this is significant considering that, during World War II, U.S. Navy veterans were exposed to chrysotile, amosite, and crocidolite that were used extensively in military ship construction. Furthermore, it was revealed that many of these shipyard workers had only recently come to medical attention because the latent period for asbestos-related diseases varies from 10 to 45 or more years between first exposure and development of disease. Also of significance is that the exposure to asbestos may be brief (as little as a month or two) or indirect (bystander disease). Department of Veterans Affairs, Veteran's Benefits Administration, Manual M21-1, Part 6, Chapter 7, Subchapter IV, § 7.21 b. In Dyment v. West, 13 Vet. App. 141, 145 (1999), the Court found that provisions in former paragraph 7.68 (predecessor to paragraph 7.21) of VBA Manual M21-1, Part VI, did not create a presumption of exposure to asbestos. Medical-nexus evidence is required in claims for asbestos related disease related to alleged asbestos exposure in service. VA O.G.C. Prec. Op. No. 04-00. Service connection - radiation exposure Service connection for conditions claimed to be due to exposure to ionizing radiation in service can be established in any of three different ways. See Davis v. Brown, 10 Vet. App. 209, 211 (1997); Rucker v. Brown, 10 Vet. App. 67, 71 (1997). First, there are diseases that are presumptively service connected in radiation-exposed veterans under 38 U.S.C.A. § 1112(c) and 38 C.F.R. § 3.309(d). Second, service connection can be established under 38 C.F.R. § 3.303(d) with the assistance of the procedural advantages prescribed in 38 C.F.R. § 3.311, if the condition at issue is a radiogenic disease. Third, direct service connection can be established under 38 C.F.R. § 3.303(d) by showing that the disease was incurred during or aggravated by service without regard to the statutory presumptions. See Combee v. Brown, 34 F.3d 1039, 1043-44 (Fed. Cir. 1994). Under Combee, VA must not only determine whether a veteran had a disability recognized by VA as being etiologically related to exposure to ionizing radiation, but must also determine whether the disability was otherwise the result of active service. In other words, the fact that the requirements of a presumptive regulation are not met does not in and of itself preclude a claimant from establishing service connection by way of proof of actual direct causation. If a claimant does not qualify as a "radiation-exposed veteran" under 38 C.F.R. § 3.309(d)(3), the veteran may still benefit from the special development procedures provided in 38 C.F.R. § 3.311 if the veteran suffers from a radiogenic disease and claims exposure to ionizing radiation in service. Under 38 C.F.R. § 3.311, "radiogenic disease" means a disease that may be induced by ionizing radiation and shall include the following: (i) All forms of leukemia except chronic lymphatic (lymphocytic) leukemia; (ii) Thyroid cancer; (iii) Breast cancer; (iv) Lung cancer; (v) Bone cancer; (vi) Liver cancer; (vii) Skin cancer; (viii) Esophageal cancer; (ix) Stomach cancer; (x) Colon cancer; (xi) Pancreatic cancer; (xii) Kidney cancer; (xiii) Urinary bladder cancer; (xiv) Salivary gland cancer; (xv) Multiple myeloma; (xvi) Posterior subcapsular cataracts; (xvii) Non-malignant thyroid nodular disease; (xviii) Ovarian cancer; (xix) Parathyroid adenoma; (xx) Tumors of the brain and central nervous system; (xxi) Cancer of the rectum; (xxii) Lymphomas other than Hodgkin's disease; (xxiii) Prostate cancer; and (xxiv) Any other cancer. 38 C.F.R. § 3.311(b)(2). Section 3.311(b)(5) requires that colon cancer and skin cancer become manifest 5 years or more after exposure. 38 C.F.R. § 3.311(b)(5). Under the special development procedures in § 3.311(a), requires that a request be made for any available records concerning the veteran's exposure to radiation. These records normally include but may not be limited to the veteran's Record of Occupational Exposure to Ionizing Radiation (DD Form 1141), if maintained, service medical records, and other records which may contain information pertaining to the veteran's radiation dose in service. All such records will be forwarded to the Under Secretary for Health, who will be responsible for preparation of a dose estimate, to the extent feasible, based on available methodologies. 38 C.F.R. § 3.311(a)(2)(iii) (2005). Chronicity/continuity of symptomatology For the showing of chronic disease in service, there is required a combination of manifestations sufficient to identify the disease entity, and sufficient observation to establish chronicity at the time, as distinguished from merely isolated findings or a diagnosis including the word "chronic." When the disease identity is established, there is no requirement of an evidentiary showing of continuity. Continuity of symptomatology is required only where the condition noted during service is not, in fact, shown to be chronic or where the diagnosis of chronicity may be legitimately questioned. 38 C.F.R. § 3.303(b) (2004). When the fact of chronicity in service is not adequately supported, then a showing of continuity after discharge is required to support the claim. 38 C.F.R. § 3.303(b) (2004); Savage v. Gober, 10 Vet. App. 488, 495-496 (1997). In Voerth v. West, 13 Vet. App. 117, 120 (1999), the Court stated that in Savage it had clearly held that 38 C.F.R. § 3.303 does not relieve the claimant of his burden of providing a medical nexus. Analysis As discussed above, for service connection to be granted three elements must be met: (1) evidence of a current disability (2) in-service incurrence of disease (colon cancer) or injury (evidence of exposure to asbestos, radiation and chemicals respectively) and (3) evidence of a relationship between the veteran's colon cancer and any in- service disease or injury. See Hickson, supra. With respect to element (1), current disability, there is of record a diagnosis with colon cancer. Accordingly, this element is met. Turning to element (2), in-service disease or injury, the Board will separately discuss disease and injury. With respect to disease, there is no medical evidence of colon cancer in service or within the one year § 3.309(a) presumptive period after service. It appears that colon cancer was initially diagnosed in 1996, over a decade after the veteran left military service. The Board notes that the veteran did receive treatment in service for blood in the stool and reported abdominal pains in service and shortly thereafter; however, there was no diagnosis of colon cancer at that time. Specifically, a March 1984 sigmoidoscopic examination conducted by VA, shortly after the veteran retired from military service in December 1983, noted only small internal hemorrhoids. A March 1997 letter from the veteran's physician, Dr. J.G., indicated that Dr. G felt that the veteran's tumor had existed "approximately" 10 years before its diagnosis in March 1996. However, ten years prior to the veteran's diagnosis was March 1986, after the end of the presumptive period. Moreover, even if it was Dr. G.'s intent to include the period between December 1983 and December 1984 in that "approximately" 10 year period prior to march 1996, this opinion is speculative and is not adequate to support the claim. See Obert v. Brown, 5 Vet. App. 30, 33 (1993) [physician's statement that the veteran may have been having some symptoms of multiple sclerosis for many years prior to the date of diagnosis deemed speculative]; Tirpak v. Derwinski, 2 Vet. App. 609, 611 (1992) [medical evidence which merely indicates that the alleged disorder "may or may not" exist or "may or may not" be related, is too speculative to establish the presence of the claimed disorder or any such relationship]. The veteran himself contends that his colon cancer existed during service or within the one year presumptive period after service. He has indicated that he was a dental x-ray technician during service. The Board has therefore considered whether he is competent to render opinions on this medical matter. Competent medical evidence means evidence provided by a person who is qualified through education, training, or experience to offer medical diagnoses, statements, or opinions. See 38 C.F.R. § 3.159 (2005). There is nothing in the record which would lead the Board to conclude that the veteran, whose medical training appears to limited to dealing with dental X-rays, is qualified to render a medical opinion concerning colon cancer. The Board does not believe that the veteran's former occupation as a dental technician qualifies him to render competent medical opinions on matters such as medical diagnoses of disorders which are not dental in nature. See Black v. Brown, 10 Vet. App. 279, 284 (1997) [in evaluating the probative value of medical statements, the Board looks at factors such as the individual knowledge and skill in analyzing the medical data]. Moreover, 38 C.F.R. § 3.309(a) requires that the claimed disability be manifested to a compensable degree. Even if the Board assumes for the sake of argument that colon cancer existed during the one year period after service (notwithstanding the March 1984 VA examination results), there is no evidence that it caused any compensable residuals. The rectal bleeding experienced by the veteran was ascribed by competent medical evidence to hemorrhoids [which have been service connected]. Dr. G. did not point to any identifiable residuals. Thus, a compensable rating could not have been assigned. See 38 C.F.R. §§ 4.31, 4.114, Diagnostic Code 7343 (2005). The presumptive provisions of 38 C.F.R. § 3.309(a) therefore do not apply to the instant case. With respect to in-service injury, the veteran contends that this involves exposure to asbestos, chemicals and ionizing radiation. According to the July 2004 opinion of Dr. S.M, the Chief Officer of the VA Office of Public Health and Environmental Hazards and the March 2002 opinion of M.B., Ph.D., the veteran's in-service exposure to asbestos, ionizing radiation and hazardous chemicals (to include benzene) has been conceded. The Board will not dispute that finding. Accordingly, element (2), in-service incurrence of injury, has been met. The Board will discuss element (3), the relationship between service and the veteran's colon cancer with specific reference to his contentions concerning asbestos, radiation exposure, chemical exposure. Resolution of this issue requires competent medical evidence, which can be provided neither by the Board or by the veteran himself. See Colvin v. Derwinski, 1 Vet. App. 171, 175 (1991) [the Board is prohibited from exercising its own independent judgment to resolve medical questions] and Espiritu, supra. Asbestos A February 2002 opinion of M.A.B., Ph.D. is of record. In that opinion, Dr. B. found that it was not as least as likely as not based upon the evidence of record that the veteran's colon cancer was caused by or related to in-service asbestos exposure. The only suggestion in the record that the veteran's colon cancer is related to asbestos comes from the veteran himself. As has been discussed above, the veteran is not competent to render an opinion on a medical matter such as etiology. See Voerth v. West, 13 Vet. App. 117, 119 (1999) [unsupported by medical evidence, a claimant's personal belief, no matter how sincere, is not probative of a nexus to service]. Accordingly, the Board finds that the weight of the probative medical evidence is against a finding of a relationship between the veteran's in-service exposure to asbestos and his colon cancer. Radiation exposure As has been discussed above, service connection may be granted in radiation claims using three different approaches. The Board will address these in turn. (i.) Presumptive service connection - 38 C.F.R. § 3.309(d) In order to establish presumptive service connection under 38 U.S.C.A. § 1112(c) and 38 C.F.R. § 3.309(d), the veteran must have been a radiation-exposed veteran who participated in a radiation-risk activity as such terms are defined in the regulation. See 38 C.F.R. § 3.309 (d)(3). The Board notes that the veteran's diagnosed colon cancer is a presumptive disease under 38 C.F.R. § 3.309(d)(2). Therefore, if the veteran was a radiation-exposed veteran under the statute, medical nexus would be established shown on a presumptive basis without the need for a competent medical opinion, and the claim would be successful. The veteran contends that his work involving dental x-rays exposed him to radiation. The statute, however, defines radiation-risk activity with precision and does not list working on, or in proximity to, dental x-rays as a radiation- risk activity. Therefore, the veteran's in-service job responsibilities do not provide a basis for finding that he participated in a radiation-risk activity, as required by the regulation. The Board therefore finds that the presumptive provisions of 38 C.F.R. § 3.309(d) are not for application in this case. (ii.) Radiogenic diseases - 38 C.F.R. § 3.311 The provisions of 38 C.F.R. § 3.311 provide for development of claims based on a contention of (1) radiation exposure during active service and (2) post-service development of a radiogenic disease. The provisions do not give rise to a presumption of service connection, but rather establish a procedure for handling claims brought by radiation-exposed veterans. See Ramey v. Gober, 120 F.3d 1239, 1244 (Fed. Cir. 1997). Section 3.311 essentially states that a dose assessment will be made in all claims in which it is established that a radiogenic disease first became manifest after service, and it is contended that the disease resulted from radiation exposure. As noted above, the veteran has been diagnosed with colon cancer which is considered a radiogenic disease under 38 C.F.R. § 3.311 (b)(2). The Board has reviewed all of the evidence of record. As noted above, the veteran's job duties in service included working with dental x-ray equipment. The veteran was initially diagnosed with colon cancer in March 1996, that is to say more than five years after his separation from service. In accordance with the provisions of 38 C.F.R. § 3.311, the RO forwarded the case to the Under Secretary for Benefits who requested an opinion from the Under Secretary for Health as to the relationship between the veteran's disability and his exposure to ionizing radiation in service. In her March 2002 memorandum, S.M., M.D, the VA Chief Public Health and Environmental Hazards Officer, opined that there was little likelihood of any relationship between the veteran's in- service radiation exposure and his colon cancer. Citing to literature concerning the effects of exposure to ionizing radiation, she observed that the instance of colon cancer among populations with radiation exposure level similar to the veteran's appeared to be relatively low. Considering this and the dose assessment of record, Dr S.M. concluded that it was unlikely that the veteran's colon cancer could be attributed to exposure to ionizing radiation in service. A March 2002 advisory opinion from the office of the Director of the Compensation Services concurred with Dr. S.M.'s opinion. It therefore appears that the requirements of 38 C.F.R. § 3.311 have been duly satisfied. Once a claim has been fully developed pursuant to the procedures set forth in 38 C.F.R. § 3.311, as it has been here, it remains the Board's responsibility to evaluate the evidence and determine whether the veteran's colon cancer was in fact the result of exposure to ionizing radiation. The question which must be answered by the Board, therefore, is whether there is a nexus between the veteran's diagnosis of colon cancer and his exposure to ionizing radiation in service. However, the record on appeal which speaks to this question consists only of the veteran's own contentions and the medical opinion described above. With respect to the veteran's own contentions that colon cancer was incurred due to in-service radiation exposure, as discussed above, although the veteran can be presumed to have limited medical knowledge due to his experience in the dental field, the Board finds that he is not competent to comment on medical matters, such as medical nexus, unrelated to dental conditions. Therefore, the only medical evidence of record on this point, the March 2002 opinion of Dr. S.M., is against the finding of a nexus between in-service ionizing radiation exposure and the veteran's colon cancer. Dr. S.M., who has a Master of Public Health Degree as well as an M.D. degree, was the VA Chief Public Health and Environmental Hazards Officer and thus is well versed in matters related to radiation exposure. Her opinion was based on the evidence of record as well as her review of the medical literature. There is no competent medical opinion to the contrary. (iii.) Combee considerations - 38 C.F.R. § 3.303(d) Notwithstanding the foregoing, the United States Court of Appeals for the Federal Circuit in Combee determined that the regulations governing presumptive service connection for radiation exposure do not preclude a veteran from establishing service connection with proof of actual direct causation. See Combee, 34 F.3d at 1043-1044; see also 38 C.F.R. § 3.303 (d). As has been discussed above, the medical evidence of record does not include competent medical evidence which indicates a positive nexus between the veteran's documented disability and in-service radiation exposure. The only competent medical opinion of record, that of Dr. S.M., is against the claim. Chemical exposure The Board has also considered the veteran's claim of causation of colon cancer due to in-service chemical exposure, to include exposure to benzene and xylene, among others. In July 2004, the veteran's file was again referred to S.M., M.D, the VA Chief Public Health and Environmental Hazards Officer. In her July 2004 opinion, Dr. M. acknowledged the veteran's in-service exposure to various chemicals but determined, based upon several medical studies from the National Academies of Science Institute of Medicine, that there was conflicting scientific data regarding the existence of a relationship between benzene, xylene and toluene and colon cancer. Dr. M. indicated: "in our opinion, it is possible that the colon cancer diagnosed in this veteran could be related to exposure to benzene and toluene while he was on active military service. However, we cannot state that it is as likely more likely as not that [the veteran's] case of colon cancer was the result of his exposure to those chemicals during his military service". This statement is virtually a verbatim replication of an opinion rendered by M.B., Ph.D. in February 2002. After having carefully reviewed the opinions of both Dr. M.B. and Dr. S.M., the Board concluded that although they are hardly models of clarity, the conclusions rendered was that that it was less likely than not that the chemical exposure caused the colon cancer. In other words, both experts reached a conclusion (which was unfavorable to the veteran's claim) rather than reaching no conclusion at all. Cf. Obert v. Brown, 5 Vet. App. 30, 33 (1993); Tirpak v. Derwinski, 2 Vet. App. 609, 611 (1992) [medical opinions which are inconclusive in nature cannot support a claim.] The veteran's own contentions of a relationship between his cancer and his chemical exposure are not probative for the reasons discussed above. See Cromley v. Brown, 7 Vet. App. 376, 379 (1995). Therefore, as there is no competent medical evidence in favor of the veteran's claim, and based on the two opinions against the claim, evidence preponderates against the veteran's claim as to this theory of entitlement. Continuity of symptomatology Based upon the veteran's contentions, the Board has also considered the provisions of 38 C.F.R. § 3.303(b), relating to chronicity and continuity of symptomatology. This amounts to an alternative method of establishing nexus to service. However, setting aside the brief, conclusory and speculative opinion of Dr. G., discussed above, there is no objective medical evidence of colon cancer in service or for over a decade thereafter. Indeed, it is undisputed the initial diagnosis of colon cancer was in 1996, over a decade after service, and there medical record do not refer to any specific symptomatology consistent with colon cancer prior to that time. As was discussed above, rectal bleeding in and shortly after service was ascribed to hemorrhoids (which in fact have been service connected). Supporting medical evidence is required. See Voerth v. West, 13 Vet. App. 117, 120-1 (1999) [there must be medical evidence on file demonstrating a relationship between the veteran's current disability and the claimed continuous symptomatology, unless such a relationship is one as to which a lay person's observation is competent]. Such evidence is lacking in this case. Continuity of symptomatology after service is therefore also not demonstrated. Accordingly, for the reasons and bases set out above, the Board has determined that medical nexus is not found for any of the veteran's theories of causation between events in service including asbestos exposure, radiation exposure, chemical exposure and abdominal symptomatology and his colon cancer. Conclusion In conclusion, for reasons and bases expressed above the Board concludes that a preponderance of the evidence is against the veteran's claim. The benefits sought on appeal are therefore denied. ORDER Entitlement to service connection of colon cancer, including claimed as secondary to asbestos, chemical and ionizing radiation exposure, is denied. ____________________________________________ Barry F. Bohan Veterans Law Judge, Board of Veterans' Appeals Department of Veterans Affairs