eP274 - Unexpected Invaders: Rare Metastases to the Colon and Rectum

Purpose/Background: Colorectal cancer is the third most common malignancy worldwide and the second leading cause of cancer-related deaths. Metastatic disease to the colon and rectum, however, is a rare entity representing approximately 1% of all colorectal cancers. Metastatic renal cell carcinoma (RCC) and lung cancer (LC) to the colon and rectum are especially rare. Less than 15 cases of metastatic RCC to the colon have been reported in the literature, and a study of over 5,000 lung cancer patients reported a 0.1% incidence of colon and rectal metastases. We present two patients diagnosed with these rare pathologies.Methods/Interventions: Patient A had a history of metastatic RCC and patient B had a history of metastatic LC. Colorectal involvement in both patients was diagnosed via colonoscopy.Results/Outcomes: Patient A is a 51-year-old male with a history of metastatic RCC with diffuse bone metastases who presented to the emergency room with bloody mucoid stool. Computed tomography (CT) scan was concerning for a sigmoid mass (Figure 1). Subsequent diagnostic colonoscopy revealed a malignant-appearing ulcerated lesion in the distal sigmoid colon, occupying a third of the luminal circumference (Figure 2). Biopsies revealed a submucosal neoplasm with pleomorphic cells with irregular hyperchromatic nuclei and prominent nucleoli, and immunohistochemical staining was positive for PAX8 and vimentin (Figure 3). These findings were consistent with metastatic RCC. Continued oncologic treatment was recommended.

Patient B is a 73-year-old male with a history of cigarette smoking and metastatic left lung adenocarcinoma. He was treated with two years of immunotherapy followed by a period of observation. Subsequent positron emission tomography (PET) scan was concerning for a fluorodeoxyglucose (FDG)-avid rectal lesion (Figure 1). Further evaluation with colonoscopy revealed an ulcerated mass of the distal rectum (Figure 2), confirmed to be malignant on biopsies. Immunohistochemical staining was positive for cytokeratin (CK) 7 and thyroid transcription factor-1 (TTF-1), and negative for gastrointestinal (GI) markers CK 20 and CDX2, consistent with metastatic lung adenocarcinoma (Figure 4). Immunotherapy was resumed, with palliative radiation to symptomatic rib lesions.Conclusion/

Discussion: Primary renal and lung cancer with metastases to the colon and rectum are extremely rare with a limited number of reported cases in the literature. In a setting of established malignancy, the development of new-onset GI symptoms should warrant workup for metastatic colorectal involvement. Resection in these cases is usually palliative and reserved for complications such as obstruction, hemorrhage, or perforation. Management is complex and should involve a multidisciplinary approach."Figure 1.

CT scan showing a sigmoid mass (patient A), and PET scan showing an FDG-avid rectal lesion (patient B).
Figure 2.

Colonoscopic views of the metastatic colon (left) and rectal (right) lesions.
Figure 3.

Histopathology of the metastatic RCC; A: H&E stain, B: PAX8 stain, C: Vimentin stain.
Figure 4.

Histopathology of the metastatic LC; A & B: H&E stain, C: TTF-1 stain.
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