Primary cancers of the appendix are rare, with an incidence of approximately 1.2 cases per 100,000 people per year and this tumor is difficult to diagnose preoperatively. The purpose of this paper is to present a rare case of metastatic mucinous carcinoma of the appendix and to provide a high index of suspicion to patients presenting with the same history, signs, and symptoms.

We present a case of a 33-year-old Filipina who reported abdominal pain and right lower quadrant mass. Following several preoperative diagnostic tests, a colonoscopy revealed synchronous tumors in various locations, prompting the need for an exploratory laparotomy to evaluate the abdomen. Histopathological examination was performed to confirm the final diagnosis which revealed primary mucinous carcinoma of the appendix. The tumor had extended into adjacent structures, including the cecal colon, ileum, and right ureter. Metastatic lesions were also identified in the descending and sigmoid colon. The disease was classified as stage IVC (T4b, N1c, M1c), indicating advanced progression with both extensive local invasion and distant metastasis.

Histopathology remains the gold standard for cancer diagnosis. Given the rarity and complexity of appendiceal mucinous carcinoma, a multidisciplinary approach is also essential. This collaborative strategy from various specialties is vital not only for achieving an accurate diagnosis but also for developing and implementing an effective, individualized treatment plan that addresses the distinct challenges of this uncommon malignancy.