cells move from the skin into other organs and the bloodstream; this progression is referred to as "leukemic mycosis fungoides", "Sézary syndrome preceded by mycosis fungoides", or "secondary mycosis fungoides". Cause Mycosis fungoides is caused by abnormal white blood cells (T-lymphocytes). These abnormal cells have a preference for localizing and proliferating uncontrolled in the outer layer of the skin (epidermis). The abnormal cells may later involve other organs such as the lymph nodes. It is hypothesized that the genetic mutations in these cancer cells lead to increased growth and escape from programmed cell death. Additionally, the disease is an unusual expression of CD4 T cells, a part of the immune system. These T cells are skin-associated, meaning they are biochemically and biologically most related to the skin, in a dynamic manner. Mycosis fungoides is the most common type of cutaneous T-cell lymphoma (CTCL), but there are many other types of CTCL that have nothing to do with mycosis fungoides and these disorders are treated differently. Diagnosis Diagnosis often requires a combination of clinical and pathological studies. Diagnosis is sometimes difficult because the early phases of the disease often resemble inflammatory dermatoses (such as eczema, psoriasis, lichenoid dermatoses including lichen planus, vitiligo, and chronic cutaneous lupus erythematosus), as well as other cutaneous lymphomas. Several biopsies are recommended, as the key microscopic features are often absent in early MF, and a complete diagnosis requires a combination of clinical and histological study. Furthermore, long periods of treatment can alter the biopsy findings, making it difficult to distinguish from other inflammatory dermatoses. Childhood Mycosis fungoides makes up 0.5% to 7.0% of cases. Although data on childhood MF is limited, a 2021 systematic review observed that there is a significant delay in the diagnosis of childhood MF which may negatively affect a child’s prognosis. Notably, most pediatric persons with MF present with early-stage disease. Histology The criteria for the disease are established on the skin biopsy by the presence of the following: Presence of cancer cells with twisted contours (cerebriform nuclei) In the patch and plaque stages, the cancer cells are seen in the epidermis (the most superficial layer of skin). This is referred to as epidermotropism. Pautrier's microabcesses, aggregates of four or more atypical lymphocytes arranged in the epidermis. Pautrier microabcesses are characteristic of mycosis fungoides but are generally absent. In the tumour stage, the cancer cells move into the dermis (the deeper layer