Expression and Clinical Significance of Somatostatin Receptor 2 in Medullary Thyroid Carcinoma

Somatostatin receptor 2 (SSTR2) has important diagnostic and therapeutic implications in neuroendocrine tumors, but studies on its expression and clinical significance in medullary thyroid carcinoma (MTC) remain limited with inconsistent findings.

SSTR2 expression was evaluated in 75 MTC patients using two scoring methods: the percentage of positive tumor cells and the H-score. Its associations with clinicopathological features were then analyzed. These results were derived from both manual assessment by pathologists and validated using an automated digital analysis platform.

Of 75 cases, 61.3% (46) were SSTR2-positive (>5% positive cells), with a median manual H-score of 0.15 (range 0-2.7). A higher manual H-score was associated with octreotide scintigraphy positivity (P = 0.019). Within SSTR2-positive cases, lymph node metastasis decreased from low to high expression (80.0% vs. 73.3% vs. 27.3%, P = 0.015), and the median manual H-score was lower in high-grade than in low-grade tumors (0.00 vs. 0.25, P = 0.010). In univariate analysis, patients with non-high SSTR2 expression (≤50% positive cells) had higher odds of elevated calcitonin at final follow-up (OR 4.17, P = 0.047). Digital and manual assessments showed directionally consistent clinicopathological associations, and the digital H-score correlated strongly with the manual H-score (Spearman ρ = 0.778, P < 0.001).

SSTR2 expression in MTC varies widely between patients. High SSTR2 expression appears associated with reduced tumor aggressiveness and a higher likelihood of biochemical cure.