Highly proliferative anal neuroendocrine carcinoma: molecular and clinical features of a rare, recurrent case in complete remission.

backgroundPoorly differentiated anal neuroendocrine carcinomas (ANECs) are rare lesions with poor prognosis, and the molecular etiology is only partially understood. CASE PRESENTATION: At our institution, we have treated and followed a patient with such a rare ANEC. He had primarily surgery followed by three rounds of repeated surgery for loco-regional recurrences. He also received three different combinations of chemotherapy and external beam radiation. At last follow-up 13 years since the primary diagnosis, the patient had been in complete remission for nine years. The patient's medical files were re-examined, including laboratory, radiology and clinical examinations. Histopathology was re-assessed, and expanded immunohistochemistry was performed from tissue specimens from the four surgical procedures. In addition, the molecular genetic status was evaluated through next-generation sequencing. The initial tumor was consistent with a 59 mm small cell neuroendocrine cancer with a Ki-67 index of 80%. Regional lymph node metastases were evident, and immunohistochemistry supported a neuroendocrine origin. A PCR screening detected human papilloma virus type 45 DNA (high-risk subtype), and focused next-generation sequencing found a missense mutation in the Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA) gene. In tissues representing subsequent recurrences, the Chromogranin A expression was lost, and the Ki-67 index increased to 90%.

conclusionsFor the first time, we report the detection of HPV45 in a case of ANEC. To our belief, PIK3CA mutations have also not been previously demonstrated in this tumor entity. In highly malignant ANECs, cure can in rare cases be achieved. Although speculative, expression of HPV45 and/or the PIK3CA mutation may have contributed to the favorable outcome.