Stage 4 small cell lung cancer: response to carboplatin, etoposide, and atezolizumab

What happened, in summary

A 55-year-old man with obesity, prediabetes, and a 30-pack-year smoking history came to the emergency department after 3 days of nausea, vomiting, abdominal pain, and constipation. He had made similar but milder emergency visits in the preceding weeks. Examination showed tachycardia, a distended mildly tender abdomen, and overactive bowel sounds. Initial testing showed mild inflammation, while stool testing and infectious workup were unrevealing. CT of the abdomen and pelvis suggested small-bowel obstruction, but upper and lower endoscopy did not find a clear obstructing lesion. MR enterography raised concern for a systemic process, prompting CT imaging of the chest, abdomen, and pelvis. Chest CT showed a solid infiltrative right hilar soft-tissue mass invading the mediastinum. Bronchoscopy was inconclusive, but EBUS-guided fine-needle aspiration of right hilar and subcarinal lymph nodes confirmed metastatic small-cell lung cancer. Malignant cells stained positive for neuroendocrine markers CD56 and synaptophysin. PET/CT showed extensive-stage disease with uptake in the right hilar mass, left adrenal gland, mesenteric lymph nodes, and bowel. The bowel symptoms were treated as chronic intestinal pseudo-obstruction related to SCLC rather than a straightforward mechanical blockage. He started first-line carboplatin, etoposide, and atezolizumab. After 3 cycles, PET showed a good response, with decreased thoracic and adrenal activity, resolution of the previously intense segmental small-bowel uptake, and only a 1 cm residual focus. His bowel-obstruction symptoms and overall wellbeing also improved. Longer-term treatment durability was not reported in the available case record. He had initially improved with conservative bowel-obstruction management and was discharged before MR enterography and CT led clinicians back to an underlying cancer diagnosis, making the presentation diagnostically challenging.