[…]2. Significance of publication of the paper and the issue of screening effect and the overdiagnosis discourse
This analysis revealed that thyroid cancer incidence within three years of the accident increased by several tens of times in Fukushima residents who were age 18 or younger at the time of the accident in comparison to the Japanese annual incidence, and that it would be impossible to attribute the increase to reasons other than radiation, such as the screening effect or overdiagnosis. According to discussions by some specialists, screening effect refers to detection of so-called “true cancer” 2-3 years earlier than it would be diagnosed clinically. Overdiagnosis refers to detection due to screening of so-called “false cancer,” or a mass of cancer cells, which may never be clinically diagnosed as cancer in life. In many of the ongoing discussions, these two — screening effect and overdiagnosis — are collectively called “screening effect,” with its meaning mainly referring to the definition of “overdiagnosis” stated above.
Our analysis reveals that the thyroid cancer incidence at the end of 2014 far exceeds the 15-year thyroid cancer risk estimated in the WHO Health risk assessment from the nuclear accident after the 2011 Great East Japan earthquake and tsunami released in late February 2013. Moreover, while a tendency towards excess occurrence of thyroid cancer was beginning to be observed in Chernobyl in 1987 — the year after the accident, this analysis actually showed ultrasound screening allowed detection of an increased incidence of thyroid cancer within one year.
I will now explain why the screening effect and overdiagnosis are not valid explanations for excess detection of thyroid cancer cases. First, the thyroid cancer incidence rate calculated in our analysis is 20-50 times the pre-accident rate. This is an order of magnitude higher than the increased incidence in thyroid cancer due to causes other than radiation exposure reported in the past. The effect generally called “screening effect” results in the incidence rate about several times higher than the pre-screening rate in cancers including thyroid cancer. It is impossible to explain the increased incidence this high by causes other than radiation.
Next, despite repeated statements that there is no precedence of mass screening and follow-ups in populations with little exposure such as Initial Screening in Fukushima, studies have been published on the results of ultrasound screening in Chernobyl conducted in children and adolescents who were conceived and born post-accident or who lived in areas with relatively low levels of contamination. A total of 47,203 underwent screening, with not a single case of thyroid cancer detected. Although the age range slightly differs from screening in Fukushima Prefecture, this result cannot be explained by differences in the level of sophistication of ultrasound equipment in detecting 5 mm nodules.
*1: Demidchik YE et al. : Childhood thyroid cancer in Belarus, Russia and Ukraine after Chernobyl and at present.
Arq Bras Endocrinol Metab 2007; 51: 748-762.
*2: Shibata Y et al: 15 years after Chernobyl: new evidence of thyroid cancer. Lancet 2001; 358: 1956-1966.
*3: Ito M et al: Childhood thyroid diseases around Chernobyl evaluated by ultrasound examination and fine needle aspiration cytology. Thyroid 1995; 5(5): 365-368.
Moreover, geographical variations in cancer detection rates (prevalence rates) within Fukushima Prefecture cannot be explained by the screening effect or overdiagnosis. Also, the emerging results of the second round screening point to the increased incidence rate which is already about 20 times higher than the pre-accident rate even under the assumption of large underestimation. When data released on August 31, 2015 are analyzed by areas and districts, it becomes apparent incidence rates in some areas and districts are beginning to exceed the first round incidence rates. As cases detected due to screening effect and overdiagnosis should have been harvested (harvesting effect), it is suggested the effect of radiation exposure due to the accident is beginning to appear within Fukushima Prefecture.
In addition to overdiagnosis, a claim of overtreatment is often made. However, the post-surgical data of thyroid cancer cases operated at Fukushima Medical University, shows there is no evidence that premature or excessive surgeries were conducted, with the exception of 3 cases where patients and/or their families opted for voluntary surgery despite an option of non-surgical observational follow-up. Rather, the data suggests the fast progression of cancer in the operated cases. I am going to introduce an excerpt of the document titled, “Regarding Surgically Indicated Cases,” released by Professor Shinichi Suzuki of Fukushima Medical University.
“As of March 31, 2015, 104 among those eligible for thyroid examination underwent surgery after being diagnosed to have “malignant or suspicious” tumors in the confirmatory examination. 97 cases were operated on at the Division of Thyroid and Endocrine Surgery, Fukushima Medical University and 7 at other facilities. As 1 of 97 cases turned out to be a benign nodule post-operatively, 96 thyroid cancer cases are discussed here. According to the pathological evaluation, 93 cases were papillary thyroid cancer and 3 were poorly differentiated thyroid cancer. (…) The post-surgical pathological diagnosis revealed 28 cases (29%) with tumor diameter ≤ 10 mm, excluding 14 cases with mild extrathyroidal extension. And 8 cases (8%) had no lymph node metastasis, extrathyroidal extension, or distant metastasis (pT1a pN0 M0). Of all 96 cases, mild extrathyroidal extension (pEX1) was seen in 38 cases (39%), and lymph node metastasis was positive in 72 cases (74%). “
3. Perspectives and reactions of international epidemiologists
Starting with the WHO Health risk assessment, the majority of experts expected an increase in thyroid cancer incidence in Fukushima Prefecture after the accident. As a result, there was no strong opposition to the results of our analysis. We have analyzed newly released data and presented the results at the annual conferences of the International Society for Environmental Epidemiology (ISEE) in Basel in 2013, Seattle in 2014, and San Paulo in 2015. Our presentation drew a big interest, and the results of our analysis have been accepted without any issues other than astonishment about how high the rate is. This reaction made us feel that there is a large gap between the international expert opinions and the explanation of screening effect and overdiagnosis in Japan.
◇Tsuda Toshihide via “Nucléaire et Faibles doses,” CNRS, Paris
◇Thyroid Cancer Detection by Ultrasound Among Residents Ages 18 Years and Younger in Fukushima, Japan: 2011 to 2014. via Epidemiology