NF1 and neoplasm: It was suggested that this phenomenon may be due to increased immune surveillance in the heterozygous tumor suppressor condition as loss of 1 copy of the NF1 gene is sufficient to enhance T cell proliferation and function.8, 9, 10 Melanoma is an immune-responsive tumor, thus in an NF1-heterozygous context, this malignancy would be less likely to develop.