Thyroid profile during the alternative Sunitinib dosing 2/1 schedule in metastatic renal cell carcinoma

Purpose: Hypothyroidism is a common side effect of Sunitinib (SUN) treatment in metastatic renal cell carcinoma (mRCC) patients. We aimed to evaluate thyroid profile during the alternative 2/1 SUN treatment schedule and to assess the predictive value of hypothyroidism in terms of survival. Methods: We performed a prospective observational study enrolling 42 consecutive mRCC patients starting first-line alternative SUN dosing 2/1 schedule. Thyroid function was assessed at baseline and during the first three SUN cycles (1 cycle = 6 weeks = 2 ON/1 OFF + 2 ON/1 OFF), and then after 6 and 12 months. Thyroid ultrasound was performed at baseline and after 3, 6, and 12 months. Results: Subclinical hypothyroidism developed in 24% of patients during the first cycle; in other 24% in the second cycle and in 14% in the third cycle. The highest TSH values were reached during the second cycle, ON phase (6.58 ± 5.74 μI U/l). We observed a reduction in thyroid size, in echogenicity and in parenchymal perfusion in all patients. Progression-free survival (PFS) tended to be longer in patients with TSH ≥ 5 μI U/ml during the second cycle (p = 0.069). TSH level was an independent risk factor for PFS in men (p = 0.009) but not in women (p = 0.285). Conclusions: This is the first study investigating functional and morphological effects on thyroid during the alternative 2/1 SUN schedule in mRCC patients. We detected an early onset of subclinical hypothyroidism, observing the association between TSH ≥ 5 μI U/ml and: (i) longer PFS in men; (ii) progressive decrease of thyroid size in absence of significant changes in autoimmune thyroid profile.