Revealing the Unanticipated: An Uncommon Case of Colorectal Adenocarcinoma Transitioning to Choriocarcinoma - A Case Report and Literature Review.

Choriocarcinomas are uncommon tumors, with non-gestational types occurring in both males and females. Primary choriocarcinoma of the colon is extremely rare. It presents significant diagnostic and therapeutic challenges due to its aggressive nature and poor prognosis, with no cure available, and a mean survival of 8 months. This case report describes a 48-year-old woman who presented with abdominal pain and an ovarian mass, initially suspected to be ovarian cancer. Further workup showed a primary tumor in the colon, with extension to the ovary and liver metastasis. The pathology findings confirmed the presence of colorectal adenocarcinoma with choriocarcinomatous differentiation, as indicated by immunohistochemistry. The patient initially responded to the cisplatin/etoposide regimen; however, she relapsed shortly after. The patient received additional treatments with pembrolizumab, paclitaxel, and olaparib, which resulted in partial remission. Despite challenges during treatment, such as suspected uveitis related to immune-checkpoint inhibitors and potential interference of antibodies with beta-human chorionic gonadotropin (β-hCG) testing, the patient maintained a good performance status for over 1.5 years after being diagnosed. The case emphasizes the difficulties in treating choriocarcinomas, primarily because of their aggressiveness and the absence of standardized therapy. Our goal with this case is to draw multidisciplinary attention to this rare condition. Further studies are necessary to comprehend its clinical characteristics, prognosis factors, molecular markers, and treatment approaches. Such studies may be crucial in establishing targeted and personalized therapy.

Learning points: Primary choriocarcinoma of the colon is rare and often misdiagnosed due to its atypical presentation, complicating timely and accurate diagnosis.The aggressive nature of this tumor and lack of standardized therapy necessitates a multidisciplinary approach and personalized treatment plans, especially following relapse.Molecular profiling guided the use of immunotherapy, which showed potential but also presented challenges, highlighting the need for further research in treating this rare malignancy.