[A mass in the popliteal fossa and leucocytosis caused by a paraneoplastic leukemoid reaction].

A 65-year-old woman was referred with a mass in the right popliteal fossa, fever and leucocytosis reaching 105 x 10(9)/l. Her medical history included the excision of a melanoma from the right ankle more than 20 years before. Ultrasound, CT and positron-emission tomography showed the mass in the right knee but no other lesions. The process was drained. Histological examination ofa subcutis biopsy indicated malignancy. Due to deterioration in her clinical condition amputation of the right leg was performed after which her leucocyte count normalized. The pathology specimen revealed a high-grade undifferentiated soft tissue tumour of unclear origin. Preoperatively assessed serum levels of granulocyte-stimulating factor (G-CSF), interleukin 6 and interleukin 8 were elevated to 241, 91 and 82 pg/ml respectively. After the amputation these levels returned to almost normal. This extreme leucocyte count may be explained by a paraneoplastic leukemoid reaction. It is hypothesized that the tumour cells produce G-CSF and other cytokines causing leucocytosis. Normalisation of the cytokine levels postoperatively supports this hypothesis.