We have reported an unusual case of colon cancer in a young patient with CD, that metastasized through a fistulous tract to the terminal ileum. Colon cancer in the setting of CD is an infrequent occurrence as compared to UC [5,6]. Metastatic CRC through a fistula is a very rare disease presentation with no reports in the literature of implantation into the small bowel through an ileal-sigmoid fistulous tract. Table outlines the reported cases of CRC metastasis within the gastrointestinal tract through fistulas. Chronic intestinal inflammation such as IBD leads to a higher incidence of gastrointestinal malignancy [9,10]. A study by Axelrad et al., described an incidence ratio of 5.7 on CRC, 21 of small bowel adenocarcinoma in IBD patients; and notable for 20 to 30 fold increase risk especially for ileal carcinoma in CD compared to general population [11]. Despite his young age, unfortunately, our patient developed colon cancer, which was likely secondary to ongoing accelerated inflammation in setting of non-compliance with medical therapy.
Patients with CD are more prone to fistula formation with occurrence reported in 17-50% of CD patients. The cumulative incidence of fistulizing CD is 21% one year after diagnos that is increased to 50% after 20 years [12]. An ileal-sigmoid fistula is a rare presentation described in a surgical case report by Hurwitt and Lantino in 1957 [13]. Other etiologies of ileocolic fistulas development include surgical complications and radiotherapy [14]. Common metastatic sites of colon cancers include the liver, lungs, nervous system, and peritoneum [8]. Intra-gastrointestinal tract metastasis are also described in few cases in the past, such as a sigmoid adenocarcinoma discovered in the duodenal bulb by Iwamuro et al. [15]. The mechanism of the metastasis is suspected to be via hematogenous, translocation of tumor cells, or peritoneal spread [16]. As described in our case, CRC metastasized through a fistulous tract is an unusual mechanism of metastasis. Reported cases of intra-intestinal tract metastasis via fistula are almost always through an anal fistula or closer proximity anatomical position, as listed in table. However, there is no prior case of metastatic adenocarcinoma of sigmoid origin into ilea-sigmoid fistula reported. Treatment of the ileocolic fistula is often surgical, as they are less likely to resolve spontaneously. However, treatment is individualized for each patient, as the morphology of the fistula and course are often complicated. In our patient, in addition to surgical treatment, his extensive disease warranted chemotherapy.
In conclusion, CD is associated with a higher risk of fistula development. Few cases in the past described CRC metastasized within the gastrointestinal tract through a fistula. Intriguingly in our case, sigmoid adenocarcinoma developed and further metastasized to the ileum via the ileal-sigmoid fistula in the setting of CD. In addition to presenting a unique pathological phenomenon in IBD patients, this case raises awareness of the importance of regular follow-up and early initiation of IBD therapies.