An 8-Mm Polyp Is Worth a 1,000 Words: Metastatic Lung Cancer Within a Tubular Adenoma

Abstract

Introduction: Lung cancer is the leading cause of cancer deaths in the United States, and cases are often metastatic at the time of diagnosis. We report a case of metastatic lung cancer initially diagnosed incidentally when a metastatic lesion was found within a tubular adenoma. Case Description: A 64-year-old male with thirty pack-year smoking history presented to the hospital with left lower extremity swelling and found to have an extensive unprovoked deep vein thrombosis. He was placed on rivaroxaban. The patient returned to hospital two weeks later with painless hematochezia. Colonoscopy was performed but did not identify a source of bleeding. However, an 8 mm polyp in the sigmoid colon were resected. Pathology results revealed a tubular adenoma containing poorly differentiated adenocarcinoma invading the lamina propria, consistent with pulmonary origin (TTF1 and CK7 positive; CK20, CDX2, GATA3 and S100 negative). Subsequent CT chest/abdomen/pelvis demonstrated multiple spiculated pulmonary nodules and enlarged supraclavicular, cervical, mediastinal and hilar nodes consistent with metastatic lung cancer. Based on the mutation pattern (PD-L1 positive; EGFR/Alk/Ros unmutated), the patient received pembrolizumab as palliative treatment.1538_A Figure 1. Chromogenic photomicrograph of colonic tubular adenoma showing metastatic poorly differentiated adenocarcinoma with negative CDX2 (specific for intestinal epithelium) staining. (x10 magnification)Discussion: Lung cancer is one of the most common primary malignancies with nearly 50% distal metastasis at the time of diagnosis. However, intestinal metastases are considered quite rare. The prevalence of metastasis to GI tract varies by report from 0.5-14%. The most common histologic types are SCC and large cell. Of the potential GI tract metastasis, the most sites are the esophagus, small intestine, and stomach. When colonic metastasis are present, two-thirds of patients are symptomatic at the time of the diagnosis and most commonly describe symptoms of abdominal pain, nausea, vomiting, and weight loss. Metastases to the GI tract are most often encountered during evaluation of symptomatic cases. In the asymptomatic patient they are often found incidentally on imaging or autopsy. Distant metastasis in lung cancer confers poor prognosis. Diagnostic modalities such as colonoscopy likely do not provide mortality benefit but less is known regarding morbidity and prevention of GI complications. In conclusion, lung cancer metastasis to the colon is exceedingly rare, and this is the first reported case of a metastatic lung cancer within a colon polyp.1538_B Figure 2. Chromogenic photomicrograph of poorly differentiated carcinoma showing positive staining for TTF1 (specific for primary lung adenocarcinomas). (x20 magnification)1538_C Figure 3. Spiculated nodular opacity in the left upper lobe anteriorly in an area of focal emphysema measuring 1 cm.