Chernobyl-Related Cancer and Precancerous Lesions: Incidence Increase Vs. Late Diagnostics

Abstract

The reported incidence of thyroid cancer in children and adolescents in Soviet Union before the Chernobyl accident was lower than in other developed countries. This is not clearly recognizable from the literature because comparisons of the high incidence figures 4 years after the accident and later have been made with those from the first years after the accident, when the registered incidence had already started to increase. Considering the low pre-accident registered incidence, there was an accumulated pool of undiagnosed thyroid tumors before the accident. The percentage of more advanced cancers, larger in size and less differentiated, was higher after the accident, when the pool of neglected cancers was diagnosed due to the screening and improved diagnostics. Some of these advanced tumors found by screening were interpreted as aggressive radiogenic cancers. The same tendency might be true also for other cancers, e.g. renal cell carcinoma. Furthermore, the screening-effect, false-positivity and registration of non-exposed patients as Chernobyl victims has obviously contributed to the registered incidence increase of malignancy.

Biological Effectiveness of Ionizing Radiation: Acute vs. Protracted Exposures

“…Today, when the literature is so abundant, research quality and possible biases should be taken into account defining inclusion criteria for studies into pooled analyses, meta-analyses and reviews. For example, certain reports on Chernobyl-related thyroid cancer can be conductive to over-estimation of carcinogenic properties of radioiodine; discussed in [72].…”

Malignancies after Chernobyl Accident: What Is True and What Is Untrue

“…The above and previously published [6,7,12,47] arguments question in principle the cause-effect relationship between ionizing radiation and cancer incidence increase after the CA. With regard to pediatric TC, existence of radiogenic cases cannot be excluded, but the registered incidence increase was largely caused by factors other than radiation.…”

“…The registered incidence of pediatric TC in the former Soviet Union (SU) before the accident was low compared to other developed nations, which had obviously been caused by differences in diagnostic quality and coverage of the population by medical examinations [7]. Accordingly, there was a pool of undiagnosed TC prior to the accident.…”

“…However, the difference in the histological grade can be explained by the averagely earlier detection of malignancies in Spain compared to Ukraine. The higher microvessel density in RCC from Ukraine, as well as the higher grade and "aggressiveness" of cancers after the Chernobyl accident in general [11], were apparently caused by detection after the CA of old neglected tumors accumulated in the population, misinterpreted as radiogenic cancers [7,56,61]. It can be confirmed by the following citation: "The tumors were randomly selected (successive cases) from the laboratories of Kiev and Valencia... [tumors were] clearly more aggressive in the Ukrainian population in comparison with the Valencian cases" [62].…”

Overdiagnosis of Thyroid Cancer: Is This Not an Ethical Issue for Pathologists As Well As Radiologists and Clinicians?

“…Intensive screening, false positives, and detection of previously neglected tumors may have led to overestimation of Chernobyl-associated PTC and tumor aggressivity. 23 Increases in neither anaplastic nor poorly differentiated carcinomas are found in elderly adults who underwent childhood tonsillar or thymic irradiation. Most studies have not found thyroid cancer following external beam irradiation to be more aggressive.…”