Primary neuroendocrine carcinoma of inguinal lymph node as a plausible entity: A case report

We report primary neuroendocrine carcinoma (NEC) of the inguinal lymph node (LN) as a plausible clinical entity. Though previously controversial and suspected to alternatively represent an atypical presentation of LN metastasis from an unknown primary, we now report the third case of isolated inguinal LN NEC. The cases strongly support this diagnosis as a separate clinical entity with indolent behavior, unlike NEC that has metastasized to the LN. Our patient was a 68-year-old female who presented with an isolated left 4 cm enlarged inguinal LN. A core needle biopsy of the mass demonstrated cores of soft tissue that were diffusely infiltrated by loosely cohesive neoplastic cells in streaming cords and clusters. The cells were hyperchromatic, enlarged, and exhibited very high nucleus to cytoplasm ratio with prominent nuclear crowding, vesicular chromatin, inconspicuous to rare nucleoli, and scant cytoplasm. Mitotic activity was robust. Immunohistochemistry staining showed positivity for synaptophysin with Ki67 >80 % but was not supportive of lymphoma or Merkel cell carcinoma. The cytological diagnosis was metastatic small cell NEC. FDG-PET/CT showed intense FDG avidity of the left inguinal LN without any evidence of potential primary malignancy or distant metastatic disease. Based on 2 previous case reports with favorable outcomes, we considered primary inguinal LN NEC as a plausible diagnosis. The patient underwent surgical resection with surgical histology confirming small cell NEC in LN, and systemic therapy and radiation therapy were held off. Postoperatively, the patient has remained disease-free for 16 months. Recognition of this clinical entity is important as it carries favorable prognosis with surgery as first line therapy. Primary inguinal LN NEC should be considered in the differential diagnosis of NECs in an inguinal LN.