Insulinoma-associated Protein 1 Expression and Its Diagnostic Significance in Female Genital Tract Neuroendocrine Carcinomas

Neuroendocrine carcinomas (NECs) are rare, but aggressive malignant tumors of female genital tract, especially in uterine the cervix. Beside histologic morphology, positivity of neuroendocrine markers with immunohistochemistry plays an important role in diagnosis of NECs. Insulinoma-associated protein 1 (INSM1) is a novel marker reported to be widely expressed in a variety of neuroendocrine tumors. A previous study also suggested INSM1 has superior performance to conventional neuroendocrine markers in cervical NECs. In our present study, comparison between immunomarkers was performed in female genital tract NECs. Forty-nine patients with gynecologic NECs (4 vagina, 39 cervix, 5 endometrium, 1 ovary) were included from 1993 to 2019 at our center. Immunohistochemistry was performed with INSM1, CD56, synaptophysin (SYN), chromogranin-A (CgA), and thyroid transcription factor 1 (TTF1). The results show INSM1 has superior sensitivity and intensity compared with CD56, SYN, CgA, and TTF1 in cervical small cell NECs, but not in large cell NECs. In contrast to cervical NECs, INSM1 immunohistochemistry shows only focal and weak staining in endometrial NECs. Our result suggested INSM1 is a sensitive marker which can be used as first-line test in histologic suspicious cervical cases, especially small cell NECs. However, negative INSM1 stain does not exclude the possibility of NECs. In endometrial NECs, conventional panel with CD56, SYN, CgA has better diagnostic performance than INSM1 alone.