HUMAN RECOMBINANT STEM-CELL FACTOR INDUCES MELANOCYTIC HYPERPLASIA INSUSCEPTIBLE PATIENTS

Background: Recombinant human stem-cell factor (SCF), a cytokine actin g on hematopoietic progenitor cells, has potential for the treatment o f several hematologic and oncologic disorders. In a hematology-oncolog y phase I trial of SCF, several patients had cutaneous hyperpigmentati on at the SCF subcutaneous injection sites. Objective: Our purpose was to investigate the pathogenesis of this hyperpigmentation phenomenon. Methods: Skin biopsy specimens were obtained before, at the completio n of, and after SCF therapy and were processed for histology, immunohi stology, and electron microscopy. Results: Skin at the site of SCF inj ection had an increased number of melanocytes, increased melanocytic d endrite extension, and melanin as compared with noninjected tissue. Im munohistochemical stains revealed an increase in staining with melanoc yte-specific monoclonal antibodies HMB-45 and NKI/beteb, and a monoclo nal antibody to the receptor for SCE c-kit. Conclusion: Subcutaneous i njection of SCF results in hyperplasia of melanocytes. SCF may be usef ul in the treatment of melanocytopenic disorders, but caution may be n ecessary in patients with disorders of melanocyte proliferation.