Unexplained anemia: A case report of metachronous adenocarcinoma arising in the transverse colon following right hemicolectomy for a primary cecal carcinoma.

Metachronous colonic carcinomas arise from months to years after the resection of the first or index primary colorectal cancer. They are not a result of tumor recurrence or metastasis and likely arise as a result of the field cancerization effect. This report presents the case of a 63-year-old male patient without family history of a colorectal cancer but had an index primary adenocarcinoma of the cecum (stage IIIC) five years ago that was treated with surgical resection and adjuvant radiotherapy and chemotherapy. He presented with fatigue and anemia of 6-month duration secondary to recurrent melena, and the specific cause of which remained obscure despite intensive diagnostic workup. Recurrence of a malignancy at the previous anastomosis site was ruled out. The patient continued to have recurrent and intermittent gastrointestinal bleeding until a nuclear red blood cell scan detected a bleeding spot in the epigastric region, which actually turned out to be a second primary carcinoma (stage I) arising from an adenoma in the transverse colon. The patient underwent a left colectomy with ileosigmoid anastomosis formation. During a two-month postoperative follow-up, the patient did not experience any episode of melena or anemia. Even though metachronous colon cancers rarely present with a recurrent and intermittent gastrointestinal bleeding with melena, an aggressive workup must be aimed at ruling out a second independent malignancy in patients who are in remission after an index primary colorectal cancer resection through hemicolectomy. Any neoteric lesion found on colonoscopy in such cases should be dealt with a higher degree of suspicion. Therefore, the need for surveillance colonoscopy as recommended by the National Comprehensive Cancer Network guidelines is imperative and should be practiced in resource-limited countries.