Williams re Thyroid Growth and Cancer (These are notes shared with the Safecast community on the Safecast Radiation Discussion Google group) As many who have been fol owing this discussion already know, Sir Dil wyn Wil iams is a leading thyroid cancer specialist (an endocrine pathologist, to be exact) based at Cambridge Univ., who along with Keith Baverstock played a major role in recognizing that the increase in childhood thyroid cancer after Chernobyl was in fact due to radiation exposure, and in pushing to have protection guidelines changed to help guard against this risk. He is a leading expert in radiation-induced thyroid cancer, with decades of hands-on experience, and held in great esteem by his peers. Wil iams has not been directly involved in investigating thyroid cancers found in Fukushima, but has been fol owing the developments closely. He has rarely spoken in public about Fukushima, or written about it, but he recently published a significant paper attempting to shed light on what the Fukushima screening results indicate about thyroid carcinogenesis in general. It’s available here, but unfortunately is paywal ed: Thyroid Growth and Cancer Wil iams D., European Thyroid Journal, Vol. 4, No. 3, 2015 http://www.karger.com/Article/Abstract/437263 I want to stress again that Wil iams is an impeccable scientist and utterly unbiased. This paper is based on an award-winning lecture he gave last December to the European Thyroid Association. Wil iams has always responded quickly to questions and inquiries we have sent him, and has usual y given permission to share his opinions here and elsewhere. I’ve spoken with him about this paper, and wil quote and summarize the most relevant sections. I apologize in advance for the length. Azby Brown +++++++++++++++++++++ From our recent correspondence: “The two basic proposals, or if you like hypotheses based on a range of disparate pieces of evidence, that most thyroid cancers originate in childhood and those that have not acquired independence from the mechanisms limiting the growth of normal fol icular cel s by adulthood almost al remain as very low-grade 'cancers' throughout life have implications for the Fukushima study.” Comment: IOW, even thyroid cancers that becomes apparent in adulthood are probably present as smal tumors during childhood. Most of these smal tumors do not “escape” and grow into large tumors, but remain smal . They are extremely common.
+++++ “I think that starting the [Fukushima thyroid screening] study was justifiable, although the scope could with hindsight have been much more restricted. Having started it, resection of the cancers was the right thing to do, the criticism in the Lancet letter was not justified because it is not correct to assume that the indolent behaviour of smal PTCs in older adults wil apply to smal PTCs in children.” Comment: Wil iams has previously expressed the opinion that both the age range and geographic range of the Fukushima thyroid screening should have been much more limited. In the past he has suggested it would have been better to limit it to children under the age of 14 at time of exposure, and areas where the estimated thyroid doses were 10mGy and over. This would have resulted in a much smal er but more informative study, and more than adequate to identify possible radiogenic thyroid cancers. Contrast this with increasingly strident cal s from some who insist that the thyroid screening should be extended to older age groups and also to other prefectures (specifical y, Toshihide Tsuda, of Okayama Univ). On the other hand, while he has often expressed concern that one result of the Fukushima screening wil be overdiagnosis and overtreatment, Wil iams believes that the thyroid operations done in Fukushima so far have not been overtreatment. He considers them justified, based on the pathology of the cancers removed. +++++ “The analysis leads to the very interesting proposal that the smal PTCs detected by screening in early life represent more rapidly growing tumours which have a higher chance than those detected later of progression to clinical y significant cancers. Resecting these may reduce the incidence of clinical y significant cancers in the next decade or two.” Comment: Wil iams hypothesizes that there are actual y two kinds of thyroid tumors, one type which grows quickly and another that stays smal throughout life, and that the Fukushima screening is identifying normal, non-radiogenic thyroid cancers of the quickly growing type. Because these are being caught early, the incidence of thyroid cancer in the screened population may be reduced in coming decades. He goes on to say that, “This might be detectable, possibly only if screening was stopped in the population of the less exposed areas.” +++++ “It becomes ever more important to involve informed, influential and independent members of the Fukushima public in the decisions. I hope the paper may help a little with the information part.” Comment: I couldn’t agree more.
++++++ As a fol ow-up, I sent Wil iams the latest results (From Aug 2015), and asked “Are you stil concerned with possible over-diagnosis and over-treatment in Fukushima, however? If so, how would you characterize that concern now?” This is his response: “Thanks again for the latest info, as you said there are no major surprises. The main problems in my view lie in the future, and involve the possibility of overtreatment, continuing exacerbation in the population of fear of future radiation induced cancer, and lack of complete coverage, possibly missing cancers and giving incomplete data. The Chernobyl and ABomb evidence shows that the risk is strongly age at exposure and dose related. The older groups from the larger part of the Prefecture wil have such a low risk that the vast majority of thyroid cancers discovered in these wil represent the normal incidence. Unfortunately the recorded incidence in this group wil be affected by the personal financial implications of agreeing to treatment, assuming this is stil the case. As the population ages, the chance that a smal cancer found on scan poses any lifetime risk to the patient diminishes, and in my opinion there comes an age when the risks of treatment of a scan discovered smal papil ary cancer outweigh the risks of doing nothing. The problem is that there is no consensus as to what that age is. Also the numbers of cases found wil continue to increase as the population ages, and wil reach a point where the burden on the health services and the finance involved wil lead to pressures to reduce screening, and if this is not careful y managed wil increase mistrust among the population. I expect that some thought is already being given to this by the committee overseeing the programme.” +++++++++++++++++++++ From the paper (emphasis mine): “Evidence from Fukushima The importance of imaging techniques in determining the recorded incidence of thyroid cancer and the problems posed by the increasing frequency of detection of smal thyroid carcinomas are brought into sharp focus by the results of screening the population exposed to fal out from the 2011 Fukushima nuclear power plant accident…. …The scale of the apparent increase has led to considerable concern in the exposed population . Nodules of less than 5 mm were not subject to further investigation, so the true thyroid cancer prevalence can be assumed to be much greater. However, the evidence from age at exposure and latency suggests that the large number of thyroid cancers so far detected is not due to radiation from the accident. Comment: Wil iams has been reviewing the Fukushima thyroid screening
findings since 2012 very closely. The recent paper is based on findings available as of Dec 2014, but after reviewing results released to date, including those from August 2015, his opinion that the thyroid cancers found so are in Fukushima are not due to radiation has not changed. +++++ “After Chernobyl the risk was greatest in those who were infants at the time of the accident, fal ing rapidly with increasing age . None of the Fukushima cases so far were infants at the time of the accident, the youngest was aged 6, and the majority were adolescents  (fig. 2)“ Comment: This remains one of the strongest arguments against the Fukushima thyroid cancers discovered so far being due to radiation exposure. +++++ “The first year’s screening found a similar incidence and tumour size as other areas in subsequent years. Even with ultrasound it would seem biological y almost impossible for cel s with the initial radiation-induced mutation to acquire the additional changes needed to give a cancer and to reach a detectable size within 1 year after the accident.” Comment: This is an important observation. +++++ “The amount of radioiodine released from Fukushima is reported to be approximately one seventh of that released from Chernobyl . That UNSCEAR report has been criticised for using the lower of the estimates available , but the higher estimate is stil less than a third of that from Chernobyl, and most of the activity released from the Fukushima accident was blown out to sea. Few early direct thyroid measurements were made in the immediate aftermath of the tsunami; using reconstructed doses the maximum absorbed dose to a child’s thyroid from Fukushima fal out has been estimated as 66 mGy compared to 5,000 mGy after Chernobyl . A low level of dietary stable iodine increases the risk of radiation-induced thyroid cancer ; dietary iodide was low in the areas around Chernobyl, but is high in Japan. Each of these separate pieces of evidence suggests that the high prevalence of thyroid carcinoma found in the first 3 years was not related to the accident.” Comment: Wil iams acknowledges the uncertainties in thyroid dose estimates, and cites Baverstock's criticism of the UNSCEAR report (ref #17), but even taking these into account he considers the conclusion very strong. +++++ “In the absence of any other known cause of a massive apparent increase in thyroid cancer incidence, the current findings must
represent the normal situation, uncovered by highly sensitive ultrasound.” Comment: Again, this conclusion is supported by almost al reputable thyroid cancer experts, and has been since 2012.. +++++ “Although there is no evidence of a radiation-related increase in thyroid cancer in the first 3 years after the accident, it is likely that one will occur. The level of exposure combined with the high dietary stable iodine suggests that it wil be on a much smal er scale and with a longer latent period than after Chernobyl. One forecast suggests it could be 6% of the normal incidence .” Comment: This is a very important point. It is likely that radiation exposure wil cause an increase in thyroid cancer in Fukushima, and Wil iams uses Jacob et al’s 2014 estimate (the best done so far, though not without caveats) that the increase could be of the order of 6% over the normal incidence, and wil have a longer latency period than seen after Chernobyl. Again, an increase of 6% wil be difficult to detect, unless the screening protocols are adjusted to focus on the most at-risk cohorts, as described above. +++++ “The evidence from Fukushima shows that many more thyroid carcinomas than were previously realised must originate in early life.” Comment: This appears to be the true lesson from Fukushima so far in relation to thyroid cancer. +++++ “The questionable benefits from lobectomy, thyroidectomy, or radioiodine therapy for smal papil ary carcinomas in adults have to be balanced against the known risk of complications…. …Current guidelines should reconsider their advice on the treatment of thyroid carcinoma in view of the likely continuing increase in incidental y discovered tumours and the findings from Chernobyl and Fukushima.” Comment: IOW, Wil iams proposes that it is important from a medical and ethical point of view to careful y balance treatment to the negative consequences of treatment, in particular, to avoid unnecessary treatment of slow-growing thyroid carcinomas. As stated above, he feels that the thyroid operations carried out so far in Fukushima have been justified, but urges caution going forward. +++++ “This analysis suggests that there is a biological distinction between so-cal ed
micro- and macro-papil ary carcinomas; a separation based purely on size is not tenable.” Comment: This is probably the most medical y important hypothesis Wil iams makes in the current paper. +++++ “The choice of size as a criterion reflects the divergence in later life of those tumours with and those without escape from growth limitation. It is not applicable to smal cancers in children, and its importance in young adults is not clear. This is relevant to the treatment of screen-detected micro- carcinomas in young people, as after Fukushima. It has been suggested that resection is overtreatment since these are micro-carcinomas , but the evidence based largely on studies in older patients should not be applied to adolescents and very young adults. Follow-up studies of the cohort in Fukushima should provide very valuable evidence on the incidence of very small lesions, and the effect of resection of early micro-lesions on the later frequency of larger tumours.” Comment: One of the most important lessons to be drawn from the Fukushima thyroid survey results so far is the information it provides about the development of normal thyroid cancer. +++++++++++++++++++++