131I therapy for differentiated thyroid cancer leads to an earlier onset of menopause: results of a retrospective study.

Treatment with 131I for differentiated thyroid cancer may give a follicle-damaging radiation dose to the ovaries. This damage to the ovarian function could shorten the fertile life span and advance the natural menopause. To address this issue, we studied retrospectively the menopausal age of 130 women treated with 131I for differentiated thyroid cancer in our institution from 1974-1993. The menopausal age of women treated with 131I for differentiated thyroid cancer after total thyroidectomy and subjected to suppressive L-T4 therapy was compared with the menopausal age of a control group including 127 goitrous women who were treated with suppressive L-T4 for a comparable period of time. The cumulative therapeutic 131I dose to cancer patients ranged from 1,110-40,700 MBq (mean +/- SD, 5,308 +/- 5,483 MBq; median, 3700 MBq). All patients chosen for the study were younger than 45 yr when first treated (i.e. first administration of 131I and L-T4 for cancer patients, and institution of L-T4 therapy for goitrous patients), and older than 45 yr at the end of the study period. The menopausal status of both groups was assessed from the clinical records and compared using Kaplan-Meier survival analysis. The menopausal age of cancer women treated with 131I and suppressive L-T4 therapy was less than that of goitrous patients treated with suppressive L-T4 therapy (P < 0.001). We could not detect any relationship between menopausal age and the age at the first or last 131I dose or to the cumulative 131I dose received. These data indicate that 131I treatment is probably associated with an earlier ovarian failure in thyroid cancer patients. Conceivably, the ovarian irradiation by 131I might contribute to the process of the follicular atresia, thus inducing earlier menopause.