Abstract
RATIONALE: Rectal dedifferentiated liposarcoma (DDL) and DDL with osteosarcomatous differentiation both are extremely unwonted. In addition, there are no reports of simultaneous DDL with osteosarcoma differentiation with small cell lung cancer (SCLC) to date. Therefore, it is imperative to alert clinicians and pathologists to this extremely rare and instructive synchronous tumor. PATIENT CONCERNS: The patient was a 63-year-old male who presented with intermittent hematochezia and a swelling in the anus. Irregular masses were found on computed tomography (CT) examinations of the chest and abdomen respectively. DIAGNOSIS: The final diagnosis of synchronous occurrence of SCLC and primary rectal DDL with osteosarcomatous differentiation was established by radiological, histological, immunohistochemical and molecular findings. INTERVENTIONS: The patient underwent a puncture biopsy of the right lung mass and a complete resection of the rectal mass. OUTCOMES: The patient abandoned treatment, and multiple SCLC metastases appeared multiple metastasis 8 months after the operation. In the end, he expired suddenly due to severe cerebral hemorrhage caused by brain SCLC metastasis. LESSONS: DDL with osteosarcoma differentiation is infrequent, and its accurate diagnosis is based on morphology, immunohistochemistry and the necessary molecular tests. In rare cases, DDL occurs concurrently with other malignancies and and will be a challenge for pathologists and clinicians at this time. Accordingly, a comprehensive examination to identify possible synchronous tumors is very important in clinical practice.