Long-term outcomes of hemithyroidectomy in unexpected hereditary medullary thyroid cancer: a nationwide observational study

Total thyroidectomy (TT) is the standard surgical approach for hereditary medullary thyroid cancer (hMTC). However, it is not rare in clinical practice for patients with hMTC to initially undergo hemithyroidectomy (HT) because the hereditary nature of the disease is not recognized until after surgery, particularly during early periods when RET testing was not widely available. We identified and assembled a multicenter cohort of patients with hMTC who underwent initial HT to (1) characterize their long-term outcomes and (2) compare prognosis with those receiving TT. This retrospective multicenter study included 152 patients with hMTC from 13 referral centers across China. Biochemical response, structural recurrence-free survival (SRFS), and disease-specific survival (DSS) were compared between the HT and TT groups using Kaplan-Meier survival analysis, Firth’s logistic regression, and Firth’s Cox regression. Among 152 patients with hMTC, 20 (13.2%) underwent HT without immediate completion thyroidectomy and 132 (86.8%) underwent TT. Compared with the TT group, the HT group had a lower frequency of multifocal disease (10% vs. 75.8%, P < 0.001), while other baseline characteristics did not differ significantly. Kaplan-Meier analyses did not detect statistically significant differences in SRFS or DSS, and biochemical cure rates also did not differ significantly (all P > 0.05). Multivariable analysis identified N1b stage and preoperative calcitonin > 500 pg/mL as independent predictors of biochemical incomplete response, whereas surgical extent showed no independent association with SRFS ( P = 0.767), DSS ( P = 0.712), or biochemical response ( P = 0.636). The TT cohort was further divided into TT1 ( n = 22, 16.7%; unilateral disease without contralateral involvement) and TT2 ( n = 110, 83.3%) for an additional subgroup comparison. No statistically significant differences in SRFS, DSS, or biochemical cure rates were detected between the HT and TT1 groups (all P > 0.05). Long-term outcomes did not differ significantly between HT and TT, although the small HT sample limited definitive comparisons. Selected patients with unexpected hMTC who underwent HT without immediate completion thyroidectomy demonstrated favorable long-term outcomes. However, these clinical observations require prospective validation.