The relationship of the clinicopathological characteristics and treatment results of post-Chornobyl papillary thyroid microcarcinomas with the latency period and radiation exposure

Abstract

IntroductionA worldwide increase in the incidence of thyroid cancer during the last decades is largely due to papillary thyroid microcarcinomas (MPTCs), which are mostly low-risk tumors. In view of recent clinical recommendations to reduce the extent of surgery for low-risk thyroid cancer, and persisting uncertainty about the impact of radiation history, we set out to address whether clinicopathological characteristics and prognosis of post-Chornobyl MPTCs were changing with regard to: i) the latency period, ii) probability of causation (POC) of a tumor due to radiation, and iii) tumor size.MethodsPatients (n = 465) aged up to 50 years at diagnosis who lived in April, 1986 in six northern, most radiocontaminated regions of Ukraine were studied.ResultsLatency period was statistically significantly associated with the reduction of POC level, tumor size and the frequency of fully encapsulated MPTCs. In contrast, the frequency of oncocytic changes and the BRAFV600E mutation increased. Invasive properties and clinical follow-up results did not depend on latency except for a lower frequency of complete remission after postsurgical radioiodine therapy. The POC level was associated with more frequent extrathyroidal extension, and lymphatic/vascular invasion, less frequent oncocytic changes and BRAFV600E, and did not associate with any clinical indicator. Tumor size was negatively associated with the latency period and BRAFV600E, and had a statistically significant effect on invasive properties of MPTCs: both the integrative invasiveness score and its components such as lymphatic/vascular invasion, extrathyroidal extension and lymph node metastases increased. The frequency of total thyroidectomy, neck lymph node dissection and radioiodine therapy also increased with the larger tumor size. The duration of the latency period, POC level or tumor size did not associate with the chance of disease recurrence.DiscussionIn summary, we did not observe overall worsening of the clinicopathological features or treatment results of radiogenic MPTCs that could be associated with the latency period or POC level, suggesting that radiation history did not strongly affect those in the analyzed MPTC patients. However, the increase in the invasive properties with tumor size indicates the need for individual risk stratification for each MPTC patient, regardless of radiation history, for treatment decision-making.

Characteristics and immune checkpoint status of radioiodine-refractory recurrent papillary thyroid carcinomas from Ukrainian Chornobyl Tissue Bank donors

“…The probability of causation (POC) of a tumor by exposure to a known dose of radiation of a certain quality of a subject of a given sex and age after a definite period of latency was determined using the US NIH/NCI Division of Cancer Epidemiology and Genetics’ Interactive RadioEpidemiological Program - Probability of Cancer Causation from Radiation Version 5.7.1 software [ https://radiationcalculators.cancer.gov/irep , ( 37 )] as described in our previous works ( 38 , 39 ). In this study, the assigned share associated with the expected value of the excess relative risk was used as a POC estimate.…”

Overtreatment of Supposedly Radiogenic Cancer and Precancerous Lesions

“…Neck dissection was performed in ∼50% of the cases. 16 Of note, recurrences were recorded only in 1.3% of the cases after a median follow-up of 5.2 years. The authors noted that microcarcinomas in their series were "rather indolent" and advised "more frequent organ-preserving surgeries vs. TT even for potentially radiogenic papillary thyroid microcarcinomas."…”

“…The authors noted that microcarcinomas in their series were "rather indolent" and advised "more frequent organ-preserving surgeries vs. TT even for potentially radiogenic papillary thyroid microcarcinomas." 16 The long-term overall survival of post-Chernobyl TC patients was deemed excellent between 1990 and 2014, with 21 deaths (1.9%) among pediatric TC patients, only two from progressive carcinoma, three from other tumors, three from non-oncologic diseases and six from trauma. Seven TC patients committed suicide.…”

Radiation-Related Thyroid Cancer

“…In addition, radiation-associated PTMCs demonstrated more frequent complete remission after RAI therapy (OR 9.174, P = .008 on multivariate analysis). A consecutive study of 465 Chornobyl PTMC patients from Ukraine aged up to 50 years at diagnosis performed by the same group did not find overall worsening of the clinicopathological characteristics and of treatment results that could be associated with the duration of latency period or the probability of tumor causation due to radiation ( 187 ). These findings imply that there may be no need for special treatment for young (up to 30 years old) or middle-age (up to 50 years old) PTMC patients even with a history of radiation exposure (to 131 I).…”