Abstract
BACKGROUND: Colorectal cancer ranks third in global cancer-related mortality, often due to metastases to liver and lungs. Ovarian metastases are less common, accounting for 3.6% to 7.4% of cases. In contrast, mature ovarian teratomas are frequently benign. Tumor-to-tumor metastasis is a rare phenomenon, with a limited number of documented cases. Three cases of mature ovarian teratomas metastasizing from different cancers have been reported. This report focuses on a case of tumor-to-tumor metastasis from sigmoid colon adenocarcinoma to a mature ovarian teratoma. CASE SUMMARY: A 41-year-old Taiwanese woman with no known systemic diseases presented with lower back pain, which led to imaging revealing malignant lesions in the spine, pelvis, liver, and multiple lung metastases. She was diagnosed with sigmoid colon adenocarcinoma with metastases to the liver, lung, bone, and a left ovarian teratoma. Treatment involved radiotherapy and chemotherapy, resulting in regression of the primary tumor and stable lung and liver lesions. Due to abdominal symptoms, she underwent exploratory surgery, unveiling a mature teratoma in the left ovary with signs of metastatic adenocarcinoma. CONCLUSION: Consider resecting mature ovarian teratomas with concurrent colorectal adenocarcinoma to prevent tumor-to-tumor metastasis.