Non-identical twin sisters concordant for Langerhans cell histiocytosis and discordant for secondary acute promyelocytic leukemia

Global characteristics of childhood acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) comprises approximately 5-10% of childhood acute myeloid leukemia (AML) cases in the US. While variation in this percentage among other populations was noted previously, global patterns of childhood APL have not been thoroughly characterized. In this comprehensive review of childhood APL, we examined its geographic pattern and the potential contribution of environmental factors to observed variation. In 142 studies (spanning >60 countries) identified, variation was apparent-de novo APL represented from 2% (Switzerland) to >50% (Nicaragua) of childhood AML in different geographic regions. Because a limited number of previous studies addressed specific environmental exposures that potentially underlie childhood APL development, we gathered 28 childhood cases of therapy-related APL, which exemplified associations between prior exposures to chemotherapeutic drugs/radiation and APL diagnosis. Future population-based studies examining childhood APL patterns and the potential association with specific environmental exposures and other risk factors are needed.

Establishment of a Langerhans cell histiocytosis lesion cell line with dermal dendritic cell characteristics

A cell line named PRU-1, derived from a Langerhans cell (LC) histiocytosis (LCH) skull lesion of a 7-year-old boy, was established and characterized. PRU-1 is an adherent spindle-shaped cell line that shows no Birbeck granules on electron microscopy. Flow cytometric analysis of cells collected from the early seventh passage showed no LC phenotypes of CD1a and S100 protein. Immunostaining of PRU-1 cells also revealed no expression of LC markers but showed expression of CD11c, CD54 (ICAM-1) and CD68, which was also observed in some peripherally located cells of the original LCH lesion. The PRU-1 cells stained positive for factor XIIIa and negative for CD34, suggesting a dermal dendritic cell phenotype. Cytogenetic analyses revealed abnormalities such as 39,XY,-2,-4,-8,-12,-12,-14,add(18)(q21),20,+mar and 44,XY,-11,-14,add(18)(q21). TCRγ rearrangement in the PRU-1 cells was not amplified by PCR. Tumorigenicity was not proven by xenografting into SCID mice. A conditioned medium from PRU-1 culture induced the proliferation of peripheral blood lymphocytes as well as the activation of monocytes from a healthy donor into CD1a-positive LC-like cells. Because the phenotypic characteristics of PRU-1 differed from those of CD1a-positive abnormal LC-like cells (LCH cells), it was likely that the PRU-1 cells were derived from peripherally located cells of the LCH lesion rather than LCH cells. LCH has been regarded as a type of granulomatous neoplasm with several intermingled inflammatory cells and influenced by stimuli such as Merkel cell polyomavirus (MCPyV) infection or cigarette smoking. However, in the PRU-1 cells, MCPyV-DNA was not detected by PCR. Stromal cell-like PRU-1 cells are likely to produce some growth or differentiation factors, which may play important roles in LCH lesion formation, cell maintenance and LC-like cell induction.

Secondary acute promyelocytic leukemia following chemotherapy for non-Hodgkin's lymphoma in a child

Of the several kinds of therapy-related leukemia, therapy-related acute promyelocytic leukemia (t-APL) is most closely associated with topoisomerase II inhibitor administration for treatment of malignancies in adults. Although rare in children, the majority of therapy-related malignancies have been etoposide-related APL associated with Langerhans cell histiocytosis. The authors describe the development of t-APL after chemotherapy administered for non-Hodgkin's lymphoma (NHL) in an 8-year-old girl. One month after cessation of the 3-year chemotherapy regimen of doxorubicin and other agents but not etoposide or radiotherapy, the patient was diagnosed with t-APL with positive PML-RARA molecular abnormality. The patient attained a complete remission following treatment with all-trans retinoic acid-containing chemotherapy. Thereafter, she successfully received hematopoietic stem cell transplantation from an HLA-matched sibling donor. Development of t-APL associated with NHL in children appears to be rare.

[Langerhans and non-Langerhans histiocytosis]

Although Langerhans cell histiocytosis (LCH) was described a century ago, its cause and pathogenesis are still unknown. A wide spectrum of disease and variable clinical behavior are characteristic. The clinical varieties of this enigmatic disease range from a lethal leukemia-like disorder that primarily affects infants to a curable solitary lytic lesion of bone. LCH is a clonal proliferative disorder of histiocytes that resembles in morphology and phenotype the dendritic antigen-presenting Langerhans' cells of the skin and other organs. Despite gaps in understanding, significant improvements in the therapies for this disease have been made. Careful risk stratification is critical for the appropriate administration of therapy. Patients with good prognostic factors may need only observation as their disease spontaneously regresses, or minimal intervention. The active search for more effective treatments for patients with poor prognostic features is a major future challenge for the Histiocyte Society.