Pedunculated-type T1 colorectal carcinoma with lung carcinoma metastasis at the deepest invasive portion

We present a rare case of colorectal T1 carcinoma with metastasis of previous lung carcinoma found at the deepest invasive portion. A 61-year-old man presented with cervical lymphadenopathy 18 years after undergoing surgery for right lung carcinoma [poorly differentiated adenocarcinoma stage IIb (T3N0M0)]. Contrast-enhanced computed tomography showed enlarged lymph nodes (LNs) in the neck and mediastinal regions. Combined hybrid-F-fluorodeoxyglucose positron emission-computerized tomography showed increased radionuclide uptake in multiple cervical LNs and mediastinal LNs. LN biopsy revealed a poorly differentiated adenocarcinoma, suspected to be a metastatic tumor of the lung. Subsequent colonoscopy revealed a pedunculated-type lesion with a depressed area in the ascending colon. We performed polypectomy as total excisional biopsy; this tumor was composed mainly of moderately differentiated adenocarcinoma, partially mixed with mucinous adenocarcinoma. The pathological findings of the invasive front of the colorectal carcinoma showed poorly differentiated adenocarcinoma with a morphological pattern similar to that of the previous lung carcinoma. Furthermore, immunohistochemical results for the histological type of the deepest invasive portion of the tissue specimen were positive for thyroid transcription factor-1 but negative for Caudal-type homeobox 2. From these morphological and immunohistochemical findings, the final diagnosis was moderately differentiated lung carcinoma, pTX N3 M1b (LN, colon) Stage IV.