Spreading of acute myeloid leukemia cells by trafficking along the peripheral outflow pathway of cerebrospinal fluid.

Acute myeloid leukemia (AML) can affect not only bone marrow (BM) and peripheral blood (PB), but also the compartment of cerebrospinal fluid (CSF). Besides standard chemotherapy, specific and non-specific immunotherapy has been employed synergistically to treat AML patients. Here we report on a patient who received standard chemotherapy, unspecific immunotherapy with interleukin-2, as well as later specific CD8+ T-cell stimulation by RHAMM-R3 peptide vaccination. The patient maintained a complete remission in BM and PB, while he developed recurrent relapses in the CSF. Moreover, the patient developed a chloroma in the vicinity of neuronal sheaths during hematological CR, but high leukemia cell numbers within the CSF spaces over a long time period. This rare observation demonstrates several aspects. There is a previously unknown site of leukemia cell distribution, namely the peripheral cerebrospinal outflow pathway (PCOP). This demonstrates the ineffective therapy of this previously unknown mechanism of leukemia cell spread. The hypothesis that the PCOP is a site of physiological CSF-T-cell trafficking, and the lumen of the PCOP should be considered as an extension of the subarachnoidal spaces without closed anatomical borders is supported by this observation. The CSF spaces, but possibly specifically the PCOP, may represent a previously unknown survival niche of tumor cells within intrathecal spaces.