Natural history of thyroid cancer [Review]

Abstract

Abstract. Thyroid cancers have long been considered to arise in middle age and, after their repeated proliferation, resulting in further damage to the genome, they progress to more aggressive and lethal cancers. However, in 2014, some studies were reported that might lead to a marked change in our understanding of the natural history of thyroid cancer. A high prevalence of papillary carcinoma in the young suggested that the first initiation of thyroid cancer is likely to occur in the infantile period. Such a conclusion was also supported by a very slow growth rate of papillary microcarcinomas (PMCs) in an observation trial. The proliferation rate of PMCs was negatively correlated with the age, and surgery to remove PMCs did not contribute to reduce mortality from thyroid cancer. These findings strongly suggested the existence of self-limiting cancers, which are truly malignant but do not progress to lethal cancers, for the first time in human history. The early detection of self-limiting cancers results in overdiagnosis. Ultrasonographic screening of the thyroid in the young should be avoided. Lethal thyroid cancers, whose origin is still unknown, appear suddenly after middle age. In the elderly, thyroid cancers are a mixture of self-limiting and lethal cancers; thus, when thyroid cancer is detected, careful follow-up with examination of its growth rate is required.

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

“…19 Takano 20 offers an interesting theory about the natural history of thyroid cancer, and Japanese studies give evidence that PTC is a common childhood phenomenon. 21 Baseline US studies performed on children following the 2011 Fukushima nuclear plant accident revealed a prevalence of thyroid cancer of 37.3/100,000.…”

“…21,22 Autopsy data from Japan have shown increasing prevalence of PTC from ages 15 through 34 years with no increase thereafter. 20 Papillary carcinoma may arise from thyroblasts, grow during childhood and early adulthood, then either regress, nonlethally progress, or persist as an indolent lesion in adulthood. Lethal thyroid tumors are rare, arise in older adults, and may be of a different origin.…”

“…Lethal thyroid tumors are rare, arise in older adults, and may be of a different origin. 20 The annual incidence of anaplastic thyroid carcinoma is approximately 1 to 2 cases/million. Some anaplastic carcinomas are found to be associated with differentiated thyroid carcino-mas and, hence, assumed to have arisen within the more differentiated tumors.…”

“…This belief can generate fear that neglect of incidental PTC may lead to dedifferentiation later in life. Takano 20 has recently challenged this concept. Based on some recent theories regarding cell origins of thyroid cancer and molecular studies, the converse may occur.…”

“…Anaplastic tumors may arise from stem cells and later undergo PTC or follicular differentiation. 20 While one cannot discount dedifferentiation of PTC in the genesis of some lethal thyroid tumors, one must consider the extremely low and stable incidence of anaplastic carcinoma relative to the burgeoning rates of incidentaloma PTC. There is yet no evidence that neglect of asymptomatic, incidentaloma thyroid nodules leads to deaths from anaplastic carcinoma.…”