Metachronous primary non‑small cell lung cancer and mucinous tubular and spindle cell carcinoma of the left kidney: A case report

Multiple primary malignant tumors (MPMTs) refer to two or more independent malignancies occurring at different anatomical sites. The present study reports the first documented case of metachronous primary lung adenocarcinoma and renal mucinous tubular and spindle cell carcinoma (MTSCC). A 69-year-old man underwent a radical lobectomy for stage IIB (pT2aN1M0) lung adenocarcinoma followed by adjuvant chemotherapy. A routine 10-month postoperative follow-up computed tomography scan revealed an ill-defined left renal mass. Subsequently, a partial nephrectomy was performed. Histopathological examination confirmed MTSCC. No recurrence was observed after 3 years of surveillance. The present study is, to the best of our knowledge, the first to report the association between lung adenocarcinoma and MTSCC, which highlights the necessity to consider a new primary malignancy in cancer survivors with new lesions. The present case highlights the critical role of integrated histopathological and immunohistochemical evaluation in distinguishing rare primary cancers, such as MTSCC, from metastasis, thus guiding appropriate therapy.