Assessment of somatostatin receptor expression in patients with pulmonary and thymic neuroendocrine neoplasms. First results of a single-center study

Background. Pulmonary and thymic neuroendocrine neoplasms (NENs) are divided into a group of well-differentiated neuroendocrine tumors (NETs), including typical and atypical carcinoids (TC and AC), and a group of poorly differentiated neuroendocrine carcinomas (NECs), including large cell neuroendocrine carcinoma (LCNEC) and small cell lung cancer (SCLC). According to the 2022 WHO classification of thoracic NENs, AC are subdivided into two groups: AC with a low mitotic index (MI) (AC G2) and AC with an elevated MI (AC G3). Russian experts distinguish well-differentiated pulmonary and thymic neuroendocrine tumors (NETs), including TC (analogous to gastrointestinal NET G1), AC with Ki‑6730% (AC G3) (by analogy with gastrointestinal NET G2 and G3), and neuroendocrine carcinomas (LCNEC and SCLC). Data on the expression of somatostatin receptors (SSTR) subtypes 2 and 5 in thoracic NENs remain limited.
Aim. To compare the expression of SSTR2A and SSTR5 using immunohistochemistry (IHC) and 68Ga-DOTATATE PET/CT.
Materials and methods. The study included 173 patients with thoracic NENs. SSTR status was determined in 133 cases (76.9%): by IHC in 65.4% (n=87) and by 68Ga-DOTATATE PET/CT in 62.4% (n=83).
Results. In the TC subgroup, SSTR positivity by IHC was detected in 66.7% of cases; in AC G2–46.5%, AC G3–70%, and LCNEC – 38.5%. SSTR2A expression was the most frequently observed. Using 68Ga-DOTATATE PET/CT, SSTR positivity was detected in 82.4% of TC cases, 86% of AC G2, 100% of AC G3, and 100% of LCNEC. The discordance rate between IHC and PET/CT was 41.7% (p=0.074). Overall survival decreased with increasing Ki‑67 (p<0.001).
Conclusions. 68Ga-DOTATATE PET/CT demonstrates higher sensitivity for detecting SSTR expression, however, IHC may identify additional isolated IHC-positive cases.

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