Collision tumor of primary malignant lymphoma and adenocarcinoma in the colon diagnosed by molecular pathology: A case report and literature review

BACKGROUND: Collision tumors of primary malignant lymphoma and adenocarcinoma in the colon are rare. Primary diffuse large B-cell lymphoma (DLBCL)–adenocarcinoma collision tumors are especially rare. CASE SUMMARY: A 74-year-old woman presented with abdominal pain of 1 mo duration. Biopsy under colonoscopy revealed adenocarcinoma of the ascending colon. Subsequently, the patient underwent laparoscopic radical resection of right colon cancer with lymph node dissection. A collision tumor was found incidentally through postoperative pathological sampling. Genetic analysis showed a collision tumor of DLBCL with germinal center B-cell subtype and TP53 mutation, and adenocarcinoma arising in a tubulovillous adenoma in the colon, with BRAF mutation and mutL homolog 1 promoter methylation. The patient died 3 mo after surgery. To our knowledge, this is the 23(rd) reported case of collision tumor of colorectal adenocarcinoma and lymphoma. The mean age of the 23 patients was 73 years. The most common site was the cecum. There were 15 cases with follow-up data including 11 living and four dead with a 3-year overall survival rate of 71.5%. CONCLUSION: Based on pathological and genetic analysis, surgery combined with chemotherapy or chemoradiotherapy may have good therapeutic effects for collision tumor.