Abstract
Background
Choriocarcinoma is a malignant trophoblastic cancer. It could be gestational and non-gestational. The primary extragonadal choriocarcinoma of the colon is an exceptionally rare tumor. There are only 12 cases of this tumor described in the literature. Only four of these 12 cases are pure primary choriocarcinomas of the colon. In the other eight cases, there is an adenocarcinoma with a choriocarcinoma component. In that reason, rare case like this is advisable to be reported.
Case presentation
The purpose of this report was to systematize the existing information about the frequency, diagnosis, and treatment of primary choriocarcinoma of the colon and to present our experience with diagnostic and therapeutic approaches to this exceptionally rare and not well-known tumor.
Primary extragonadal choriocarcinoma is most frequently found in the retroperitoneal space, mediastinum, pituitary gland and, very rarely, in the gastrointestinal tract. The stomach is the most frequent localization in the gastrointestinal tract. In our case, an extended right hemicolectomy was performed according to the principles of oncologic resection. Chemotherapy for gonadal choriocarcinoma was started. At present - four months after the surgical intervention, the Bulgarian patient does not show progression of the disease and is in good general health.
Conclusion
There is still no algorithm for treatment of primary choriocarcinoma of the colon because this is an extremely rare tumor. The behavior in this type of tumors remains a challenge for clinicians.

Key words: extragonadal choriocarcinoma, rare tumor, treatment