Collision tumor of the colon – colonic adenocarcinoma and ovarian granulosa cell tumor

BACKGROUND Collision tumors of the colon are rare. We report the first case, to our knowledge in the English literature, of a collision tumor composed of a colonic adenocarcinoma arising in a sigmoid diverticulum coexisting with a recurrent ovarian granulosa cell tumor. CASE PRESENTATION A 64-year old woman presented with small bowel obstruction and a large, heterogenous, solid/cystic serosal based pelvic mass consistent with a gastrointestinal stromal tumor on imaging. Her significant past history 16-years ago included a bilateral salpingo-oophrectomy with hysterectomy. Surgical removal of the mass and pathological examination revealed the presence of a colonic adenocarcinoma arising in a large sigmoid diverticulum coexistent with a second neoplastic tumor phenotype; confirmed to be a delayed recurrent ovarian granulosa cell tumor. Though coexistent, the two tumor phenotypes respected their boundaries with no diffuse intermingling or transition between them. She developed lung metastases from the recurrent ovarian tumor within 6 months and died within a year of follow-up. CONCLUSION Collision tumors of the colon are rare. This is the first case reported of a collision tumor composed of adenocarcinoma colon and recurrent granulosa cell tumor representing an example of two independent tumors in a unique one-on-another collision. Clinical awareness and recognition of such tumors are important as they will dictate appropriate treatment strategies dependent on the individual biological aggressiveness of each of the tumor components. Our report highlights the need for histopathologists, surgeons, and oncologists to be aware of the rare possibility of collisions tumors. As seen in our case, the delayed recurrence of granulosa cell tumor of the ovary sixteen years after the initial presentation was the key determining factor in tumor recurrence, tumor progression, and tumor metastasis within three months, which ultimately lead to accelerated death within a year of clinical presentation. Thus accurate identification and recognition of the second neoplasm is important as prognosis and survival may be determined by this component as seen in our index case.