Latency period of thyroid neoplasia after radiation exposure.
OBJECTIVE
To determine the temporal sequence for developing benign and malignant thyroid neoplasms after radiation.


BACKGROUND
Therapeutic radiation is associated with thyroid neoplasms in humans and animals. Some question whether thyroid cancers develop de novo or from benign thyroid neoplasms. Little information, however, is available concerning the time to development of benign and malignant thyroid neoplasms after radiation exposure.


METHODS
We retrospectively analyzed the records of 171 consecutive patients who had a history of exposure to radiation and were treated surgically at University of California, San Francisco-affiliated hospitals for thyroid neoplasms between 1960 and 1999.


RESULTS
There were 66 men and 105 women aged 9 to 80 years (mean, 47.0 years). One hundred patients had benign and 71 had malignant tumors (58 papillary cancers, 10 follicular cancers, 1 Hurthle cell cancer, 1 medullary cancer, and 1 carcinosarcoma). The mean latency period for benign tumors was longer than that for malignant lesions (mean, 34.1 and 28.4 years, P = 0.018; median, 38.0 years and 30.0 years, P = 0.001). Follicular carcinomas developed sooner (mean, 20.5 years; median, 20 years) than did follicular adenomas (mean, 35.3 years; median, 36.5 years; P = 0.003, P = 0.0009). Patients with papillary thyroid cancers presenting as occult papillary cancers (<1 cm) and as a dominant nodule had similar latency periods (mean, 34.0 and 28.0 years P = 0.29; median, 37.5 and 30.5 years, P = 0.09), respectively.


CONCLUSIONS
Although there could be selection bias regarding referral of patients, our data document that malignant thyroid tumors after radiation exposure, including follicular carcinomas, present earlier than do benign thyroid tumors. Occult and manifest papillary thyroid cancers present at about the same time interval after radiation exposure. Our findings question whether benign thyroid neoplasms progress to malignant thyroid neoplasms and that most occult thyroid cancers do not progress to malignant thyroid cancers in radiation-exposed patients.
Kikuchi
Shoichi
S
Department of Surgery, UCSF Affiliated Hospitals, 94143-1674, USA.
Perrier
Nancy D
ND
Ituarte
Philip
P
Siperstein
Allan E
AE
Duh
Quan-Yang
QY
Clark
Orlo H
OH
D000367:Age Factors; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006042:Goiter / Q000453:epidemiology / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology / Q000473:pathology; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000453:epidemiology / Q000473:pathology; D013997:Time Factors