What happened, in summary

A 68-year-old ex-smoking man with hypertension and diabetes presented after losing more than 10 kg over 3 months. Chest X-ray showed a 6.6 x 5.1 cm mass in the right upper lung. CT then showed soft-tissue masses in both the right upper lung and spleen. CT-guided lung biopsy reported non-small cell lung cancer with positive neuroendocrine markers. Abdominal CT showed several heterogeneous contrast-enhancing low-density masses in an enlarged spleen, with the spleen measuring 20 cm. Whole-body PET showed tumor avidity in the right upper lung and enlarged spleen, consistent with splenic metastasis, and the clinical stage was cT3N1M1c. Because the splenic tumor was very large, laparoscopic surgery was considered impossible. He underwent open splenectomy with partial diaphragm resection. The removed spleen weighed 1300 g, and the splenic tumor measured 17 x 13 x 9 cm. The tumor cells were diffusely positive for TTF-1, synaptophysin, and CD56, supporting metastatic large-cell neuroendocrine carcinoma. Two months later, the primary lung tumor was surgically removed. Pathology showed mixed moderately differentiated adenocarcinoma and large-cell neuroendocrine carcinoma, with R0 resection and no regional lymph node metastasis. The final stage was pT3N0M1c, Stage IVB. He refused neoadjuvant and adjuvant systemic therapy, so follow-up proceeded with observation. After 1 year of postoperative follow-up, there was no evidence of recurrence. The splenic tumor had yellowish-white multifocal nodularity on cut surface, and removal of the primary lung tumor was planned as the second step of an interval resection strategy. Because he declined systemic therapy, surveillance is explicitly captured.