<s>[INST] My nephew has a disease called histiocytosis he s had it since he was two. He s 11 now and has some long term side effects that they keep an eye on. About a year ago he had a brown freckle-like spot on his back near his lower spine . Since then it has progressed to about ten and they re all around the same size and pretty close together. They are about 6 to 8mm in diameter each! My sister has an appt set up with dermatologist but it s a few months away! Any idea what this can be? [/INST] Hello and welcome to Chat Doctor, Histiocytes are macrophage like cells present ubiquitously in all body tissues. Histiocytes play a role in the defense mechanism of the body. They are present in the lymph nodes and cause sinus histiocytosis. Histiocytes are also present in the skin. Proliferation of these cells in the skin can cause skin lesion. The nature of the skin lesions can only be confirmed after skin biopsy. Proliferation of astrocytes in the skin biopsy will confirm the neoplastic process of the astrocytes. Appropriate Chat Doctor. Thanks and take care </s>