"Not-So-Indolent" neuroendocrine neoplasms: two case reports of gastrointestinal small cell neuroendocrine carcinomas

Small cell neuroendocrine carcinomas (SCNECs) of the gastrointestinal (GI) tract are exceedingly rare and aggressive malignancies. Unlike pulmonary SCNECs, which are well-characterized, extrapulmonary GI-SCNECs lack established diagnostic pathways and treatment algorithms due to their rarity and histopathological overlap with other poorly differentiated tumors. Literature on their clinical course remains limited to isolated reports, with scarce data on site-specific presentations. These two cases contribute to the existing literature by illustrating distinct primary GI sites (gastric and rectal), underscoring the challenges in early diagnosis and the aggressive clinical progression despite intervention.

The first patient, an 80-year-old man, presented with progressive dysphagia and dyspnea. Imaging revealed mediastinal lymphadenopathy and gastric wall thickening. Endoscopic biopsies confirmed gastric SCNEC with widespread metastases. Despite initiation of palliative care, his condition deteriorated rapidly, and he died one month after diagnosis. The second patient, a 69-year-old man, presented with significant weight loss and lower abdominal pain. Colonoscopy identified a circumferential rectal mass, and biopsies confirmed SCNEC. Staging demonstrated hepatic and nodal metastases. He received platinum-based chemotherapy and pelvic radiotherapy, achieving only transient stabilization. Following treatment cessation, his disease progressed, and despite resuming chemotherapy, he died 11 months after diagnosis.

These cases emphasize the necessity for heightened clinical suspicion of SCNEC in rapidly progressive GI malignancies, even in atypical presentations. Early recognition and multidisciplinary management are crucial, although current therapeutic options offer limited durability. By delineating site-specific clinical courses, this report contributes to the limited body of evidence on GI-SCNECs and underscores the urgent need for standardized diagnostic criteria and treatment protocols to improve outcomes.