Lung adenocarcinoma diagnosed incidentally after renal biopsy for suspected right renal cancer

We present a case of lung adenocarcinoma metastasizing to the right clear cell renal cell carcinoma diagnosed by computed tomography (CT)-guided renal biopsy and immunohistochemistry. A 72-year-old male patient had right lower abdominal pain for 3 days, followed by right loin pain for 10 days. On CT scan, renal cell cancer was suspected with multiple metastases. Renal cell cancer with metastatic lung adenocarcinoma was diagnosed on CT-guided renal biopsy with positive immunohistochemical markers. The patient, unfortunately, expired after few days of diagnosis. Tumor-to-tumor metastasis is an unusual disease, and its tumors are aggressive. A definite diagnosis of tumor-to-tumor metastasis is a clinical challenge. Immunohistochemistry helped us in the diagnosis without the primary lesion biopsy.