Retroperitoneal metastatic poorly differentiated carcinoma with β-human chorionic gonadotropin secretion presenting as a psoas abscess

RATIONALE Psoas abscesses generally arise from a contiguous intra-abdominal or pelvic infectious process or hematogenous spreading of bacteria. The serum β-human chorionic gonadotropin has been used to detect normal or ectopic pregnancy. It also can be utilized in following up carcinomas. PATIENT CONCERNS Here, we reported a case of a 47-year-old woman who presented with a left psoas mass presumptively diagnosed as an abscess secondary to lumbar tuberculosis In addition, the patient had abnormal increase of β-human chorionic gonadotropin. The computed tomography (CT) scan and magnetic resonance imaging (MRI) showed that the 5th lumbar vertebral infection or tuberculosis with left psoas abscess. CT-guided percutaneous biopsy, surgical exploration and biopsy, and F-FDG (fluorodeoxyglucose) positron emission tomography-CT (PET-CT) were used to make a definite diagnosis. The sigmoidoscopy and biopsy were used to further diagnose. DIAGNOSES The biopsy of left psoas demonstrated metastatic or infiltrating poorly differentiated carcinoma with secretion of β-human chorionic gonadotropin. The subsequent pathological examination of neoplasm showed the same pathologic morphology. INTERVENTIONS Appropriate treatment of infected retroperitoneal mass, systematic chemotherapy and cancer biotherapy for metastatic poorly differentiated carcinoma were taken. OUTCOMES Interventions provided little help until the patient died of secondary infection and multiple organ failure. LESSONS This case represents an extremely unusual clinical presentation of metastatic poorly differentiated carcinoma with secretion of β-human chorionic gonadotropin presenting as a psoas abscess. Physicians also need to sharpen their awareness of the potential malignant carcinomas mimicking psoas abscess.