Papillary microcarcinoma of the thyroid among atomic bomb survivors: tumor characteristics and radiation risk.
BACKGROUND
: Radiation exposure is an established cause of clinical thyroid cancer, but little is known about radiation effects on papillary microcarcinoma (PMC) of the thyroid, a relatively common subclinical thyroid malignancy. Because the incidence of these small thyroid cancers has been increasing, it is important to better understand them and their relation to radiation.


METHODS
: PMCs were identified in a subset of 7659 members of the Life Span Study of atomic bomb survivors who had archived autopsy or surgical materials. We conducted a pathology review of these specimens and evaluated the histological features of the tumors and the association between PMCs and thyroid radiation dose.


RESULTS
: From 1958 to 1995, 458 PMCs were detected among 313 study subjects. The majority of cancers exhibited pathologic features of papillary thyroid cancers. Overall, 81% of the PMCs were of the sclerosing variant and 91% were nonencapsulated, psammoma bodies that occurred in 13% and calcification was observed in 23%. Over 95% had papillary or papillary-follicular architecture and most displayed nuclear overlap, clear nuclei, and nuclear grooves. Several of these features increased with increasing tumor size, but no association was found with radiation dose. A significant radiation-dose response was found for the prevalence of PMCs (estimated excess odds ratio/Gy = 0.57; 95% confidence interval, 0.01-1.55), with the excess risk observed primarily among women.


CONCLUSIONS
: Exposure to low-to-moderate doses of ionizing radiation appears to increase the risk of thyroid PMCs, even when exposure occurs during adulthood. Cancer 2010. (c) 2010 American Cancer Society.
Hayashi
Yuzo
Y
Department of Pathology, Hiroshima Asa Citizens' Hospital, Hiroshima, Japan.
Lagarde
Frederic
F
Tsuda
Nobuo
N
Funamoto
Sachiyo
S
Preston
Dale L
DL
Koyama
Kojiro
K
Mabuchi
Kiyohiko
K
Ron
Elaine
E
Kodama
Kazunori
K
Tokuoka
Shoji
S
D000231:Adenocarcinoma, Papillary / Q000188:drug therapy / Q000453:epidemiology* / Q000209:etiology / Q000473:pathology; D000368:Aged; D000369:Aged, 80 and over; D001344:Autopsy; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D009689:Nuclear Warfare; D054043:Nuclear Weapons; D011839:Radiation, Ionizing; D012307:Risk Factors; D017741:Survivors; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000473:pathology