Thyroid function post supraclavicular lymph node irradiation in patients with breast cancer

INTRODUCTION: In East Africa, the estimated incidence of breast cancer is second only to cervical cancer. Supraclavicular irradiation post-modified mastectomy is crucial to breast cancer management, as it improves local control and overall survival. However, this is associated with adverse effects, including hypothyroidism (HT), which is usually under-reported. This study aim was to evaluate radiation-induced thyroid gland functional changes following treatment of supraclavicular lymph nodes in breast cancer patients.METHODS: This was a prospective descriptive study of patients with breast cancer from May 1, 2017, to May 30, 2018. Pre and post-treatment TSH, fT4, and fT3 values were compared using a Wilcoxon signed-rank test.RESULTS: A total of 42 patients were recruited for this study, with a mean age of 55.7 years (32-71). The mean baseline TSH level was 2.90 (±6.37), with a normal range of 0.27-4.2 uIU/mL. The mean T4 and T3 level were 15.77 (±4.83), with normal ranges of 10.16-22 pmol/l for T4, and 3.46 (±6.22), with a normal range of 1.06-3.3 nmol/l for T3. A Wilcoxon signed-rank test indicated that there was a statistically significant increase in mean TSH levels over baseline when measured at three, six-, and nine-months post-treatment, with p-values of 0.0047, 0.0002, and <0.0001, respectively. In total, four patients (10%) had thyroid function tests outside the normal ranges. Zero patients developed clinical HT during the time period studied.CONCLUSION: As hypothesized, supraclavicular radiation led to subclinical HT, but the incidence of clinical HT over time remains unknown.