Other namesCarcinoma cell leukemia
Carcinocythemia - malignant tumour cells in peripheral blood (cropped v1).png
A case of carcinocythemia. The large, round cells are breast cancer cells circulating in the peripheral blood.[1]
SpecialtyHematology, oncology
CausesUsually secondary to metastatic cancer in the bone marrow
Differential diagnosisAcute leukemia, lymphoma, leukemoid reaction, circulating immature cells from chemotherapy, circulating endothelial cells, megakaryocytes or osteoclasts
PrognosisPoor; 15% survival rate at 6 months

Carcinocythemia, also known as carcinoma cell leukemia,[2] is a condition in which cells from malignant tumours of non-hematopoietic origin are visible on the peripheral blood smear.[3][4] It is an extremely rare condition,[5] with 33 cases identified in the literature from 1960 to 2018.[4] Carcinocythemia typically occurs secondary to infiltration of the bone marrow by metastatic cancer[6] and carries a very poor prognosis.[3][4][5]


Carcinocythemia occurs most commonly in breast cancer, followed by small cell lung cancer, and usually appears late in the course of the disease.[4] Thrombosis and disseminated intravascular coagulation are frequently reported in association with carcinocythemia.[2][4] The prognosis is poor: a review of 26 patients found that 85% died within 6 months of the diagnosis, with an average time of 6.1 weeks between diagnosis and death.[4]

The amount of tumour cells on the blood smear can range from 1 to 80 percent of the total white blood cell count,[4] with lower percentages being more common.[3] Carcinocythemia is distinct from the presence of circulating tumour cells (CTCs), as CTCs usually occur in such low quantities that they cannot be seen on blood smear examination, requiring special techniques for detection.[2][7]

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