βhCG-secreting osteosarcoma.

A 35-year-old woman presented to our institution with tender, right knee swelling. Radiological and pathological work-up revealed metastatic osteosarcoma. Prior to the initiation of chemotherapy, she underwent a routine urine pregnancy test and was surprised with a positive result. Serum beta human chorionic gonadotropin (βhCG) levels were also consistently positive and rising. No gestational sac was seen at transvaginal ultrasound. The paraneoplastic ectopic secretion of βhCG has been well described in gestational trophoblastic and gonadal tumours but has very rarely been associated with other tumour types. This patient's βhCG level was reflective of osteosarcoma activity and normalised with response to chemotherapy. The prognostic implications of βhCG expression in more diverse tumours is unclear; however, where raised, it can be used to monitor disease activity.