Despite advances in the treatment of patients with a variety of malignancies, colon cancer with peritoneal metastases is still associated with a poor prognosis. Watanabe et al. reported that 5% of patients with colon cancer have peritoneal metastases at the time of diagnosis [2]. They also found that synchronous peritoneal metastases are associated with a poor prognosis. The present patient had peritoneal metastases at the time of an inguinal hernia repair, and the site of the primary tumor was unknown until after the colon resection. Cancer of unknown origin represents 3 to 5% of all malignant epithelial tumors [3]. Adenocarcinoma comprises approximately 70% of cancers of unknown origin. In an autopsy series, tumors of the lung, pancreas, hepatobiliary tree, and kidney account for approximately two thirds of cases of cancer of unknown primary [4]. Colon cancer is relatively rare as a site of these tumors. Colonoscopy and biopsy did not reveal the definitive diagnosis in this patient. However, PET-CT scan identified the colon as the likely origin of the peritoneal metastases, which was confirmed after resection of the colon.
Only four patients with metastatic colon cancer in an inguinal hernia sac have been reported. All of these patients were males over 60 years of age. It remains uncertain why metastases develop within a hernia sac. Roslyn et al. suggested that the mechanism might be explained by local inflammation of the sac and gravity, in a manner similar to drop metastases to the pelvic cul-de-sac [5]. Yu et al. demonstrated that inflammatory cytokines (interleukin-1β and tumor necrosis factor-α) enhanced tumor cell adhesion in biological tests [6]. The present patient did not have any trauma or previous left inguinal surgery to suggest a cause of inflammation. We hypothesize that the sigmoid colon, including the tumors in the diverticula, may have descended in the hernia sac and may have contributed to inflammation and cancer seeding. It is important to make an effort to identify the primary lesion when a metastatic nodule is found during inguinal hernia repair. However, routine studies do not have to be done before the metastasis is examined histologically because this is very rare.
Malignancies can arise in colonic diverticula. The diagnosis was made based on the endoscopic finding of a tumor within a diverticulum [7]. However, establishing the diagnosis may be complicated by abnormal findings, such as abscess formation, submucosal progression, or diverticulitis [8]. Hence, endoscopic findings may not facilitate establishing the definitive diagnosis, as in the present patient.
There are 11 previous reports of colon cancer arising in a diverticulum. Of these, nine were in an advanced at the time of diagnosis. Eight of these lesions were in the left colon. Since colonic diverticula are thin-walled and lack a muscular layer, cancers arising within a diverticulum can easily penetrate the serosa which may facilitate early development of disseminated disease. Patients with cancers arising in a diverticulum need careful evaluation and follow-up [8]. The present patient had two separate cancers in sigmoid diverticula which were considered synchronous, because the pathological characteristics were different. The proximal lesion was mainly moderately differentiated adenocarcinoma, accompanied by highly and poorly differentiated adenocarcinoma. However, the distal lesion was mainly moderately differentiated adenocarcinoma without poorly differentiated adenocarcinoma. To the best of our knowledge, the present case is the first report of two cancers in colonic diverticula.
