Case report: Exceptional long-term response to first-line chemoimmunotherapy in extensive-stage small-cell lung cancer presenting with colonic metastasis

Lung cancer remains the leading cause of cancer-related mortality worldwide, with small-cell lung cancer (SCLC) accounting for approximately 15% of cases. Owing to its aggressive biology, rapid doubling time, and early metastatic spread, SCLC carries a poor prognosis. Metastases most commonly involve the bones, liver, brain, lungs, and adrenal glands, while gastrointestinal involvement, particularly intracolonic metastasis, is exceedingly rare. The standard treatment for extensive-stage (ES) SCLC consists of platinum-based chemotherapy combined with anti–PD-L1 immunotherapy, achieving response rates of 60–70%; however, median overall survival remains approximately 12 months. We report the case of a 73-year-old man with ES-SCLC who presented with gastrointestinal bleeding due to an intraluminal colonic metastasis. He received first-line carboplatin, irinotecan, and durvalumab. After three cycles, imaging showed a partial intrathoracic response and complete resolution of the colonic lesion. The patient completed six cycles of chemoimmunotherapy, followed by consolidative radiotherapy and durvalumab maintenance. He achieved a progression-free survival of 35 months before central nervous system disease progression. This case illustrates an exceptional long-term response to first-line chemoimmunotherapy and highlights the need to consider rare gastrointestinal metastases in patients with atypical presentations.