Background Intravascular tumor thrombi are mainly found in patients with liver cancer or renal carcinoma but rarely occur in those with rectal cancer. Case presentation This is a case report of a 58-year-old woman with a swollen right lower extremity 14 months after radical resection for rectal cancer. Although ultrasonography indicated the presence of deep venous thrombosis (DVT) located in the right common iliac vein, interventional angiography showed that a circular mass, considered a tumor thrombus, was located in the right common iliac vein. The tumor thrombus was cured by interventional therapy, and the pathological report confirmed that the metastatic tumor thrombus originated from the rectal cancer. The patient underwent concurrent chemoradiotherapy and systemic therapy. However, right lung, retroperitoneum, and 2nd sacral vertebral metastases were discovered during follow-up. Conclusion The correct diagnosis of a tumor thrombus and its differentiation from DVT can prevent incorrect treatment and prolong the survival of patients with rectal cancer.

Rationale: Primary clear cell adenocarcinoma of the rectovaginal septum is a very rare event. Patient Concerns: We reported a case of a 55-year-old woman diagnosed with a lump in the vaginal rectal septum after undergoing hysterectomy with bilateral salpingo-oophorectomy in 2017, who was admitted to our department due to vaginal bleeding. Magnetic resonance imaging of the pelvis indicated the vaginal rectal space cystic and solid mass about 110 mm × 100 mm × 140 mm in size. Diagnosis: The pathological diagnosis of postoperative was clear cell adenocarcinoma. Interventions: Abdominal laparotomy showed a solid block of the vaginal rectal septum. Surgery was performed to reduce the tumor. Outcomes: This patient received 8 courses of combined chemotherapy courses after surgery for the residual lesion and achieved a complete response. Lessons: Due to the rare observation of the growth pattern, the cell morphology and immune phenotype are not specific, and clinical and pathological diagnosis is difficult. Introducing the diagnosis and treatment of this case and reviewing the literature provide a relevant reference for clinicians identification and diagnosis and treatment of this rare case.