cd7 expression in differentiating mycosis fungoides from benign cutaneous lymphocytic infiltrates

background: diagnosis of the early phase of mycosis fungoides (mf) is sometimes difficult. loss of cd7 expression is considered a distinguishing characteristic of mf. the aim of this study was to determine the range of cd7 expression in mf and compare the results with benign inflammatory dermatosis and equivocal cases of possible mf.   methods: during a period of 30 months, we examined 15 patients with mf, 12 patients suspicious for mf, and 15 patients with benign inflammatory dermatosis. the slides stained by h&e; were reviewed by two pathologists. immunostaining was done for cd43, cd3, cd5, cd7, and cd20 on paraffin embedded tissues.   results: all the patients in mf group showed absence of cd7 expression in epidermotropic mycosis cells. compared with benign inflammatory dermatosis, patients with mf had significantly lower cd7 expression in the dermal infiltrate (p< 0.0001). in patients with mf, the mean cd7 was significantly lower than cd43, cd3, and cd5 (p=0.001). the mean cd7 count of parapsoriasis was significantly higher than mf (p= 0.01). the mean cd7 count of parapsoriasis was significantly lower than benign inflammatory dermatosis (p=0.016). the lowest mean cd7 counts were found in patch stage of mf. low cd7 expression < 10 % lymphocytes had sensitivity and positive predictive values of 75% and 100% and specificity and negative predictive values of 100% and 83.3% for the diagnosis of patch stage of mf.   conclusion: minimal expression of cd7 is a specific finding for patch stage of mf. benign inflammatory dermatosis can also show low expression of this marker, but rarely matches that of patch stage of mf.