Thyroid Cancer Treatment and Subsequent Infertility Diagnosis in Female Adolescents and Young Adults: A Population-Based Cohort Study
Background: Unnecessary treatment of thyroid cancer as a result of increased surveillance may be associated with substantial side effects, including infertility, often without improvements in survival rates. Objective: To examine the association between thyroid cancer treatment and subsequent infertility diagnosis. Study Design: Population-based cohort study of female Adolescent and Young Adults (AYAs, 15-39 years) who have been treated for thyroid cancer between 1992 and 2011 in Ontario and lived at least 5 years after cancer diagnosis. Exposure data were obtained through the CIHI/DAD, which was linked to several health care data sources through ICES. Thyroid cancer treatment, from less invasive to more aggressive, was categorized as: less than total thyroidectomy-LTT, total thyroidectomy-TOT, or TOT accompanied with radioactive iodine therapy-TOT+RAI. Women were followed in the cohort until December 31, 2016. Infertility diagnosis was identified using information on physician billed claims through the OHIP database (ICD-9 628). Modified Poisson regression models were used to examine associations between type of thyroid cancer treatment and infertility diagnosis, adjusting for confounding factors. Results: From 4,926 female AYAs with thyroid cancer during the study period, 849 (17%) received LTT, 2457 (50%) TOT, 1620 (33%) TOT + RAI. Mean age at cancer diagnosis was 31.04 years (SD=5.99). The median follow-up time for cancer survivors was 10.78 years (IQR=6.96-15.77). A total of 563 (11%) had a subsequent diagnosis of infertility. The frequency of infertility diagnosis was similar among treatments (p=0.99), with a similar mean time to infertility diagnosis (p=0.69). Mean age at infertility diagnosis was 35.26 years (SD=5.48). Compared to women with LTT, women who received TOT or TOT+RAI did not have a higher risk of subsequent infertility diagnosis (RR=0.98, 95% CI: 0.78, 1.24, p=0.86; RR=0.93, 95% CI: 0.72, 1.20, p=0.55 respectively). Conclusions: More aggressive types of thyroid cancer treatment are not associated with an increased risk of infertility diagnosis when compared to the least aggressive type of treatment. Findings of this study are similar to those of others that have examined treatment effects on female reproductive outcomes. Further research is needed to elucidate whether ICD-9 628 code for female infertility is a valid measure of female infertility.