A 15cm hyperpigmented macule on an adolescent male undergoes changes such as coarseness,growth of hair acne.Dignosis is-

Becker's nevus is a unilateral, solitary, acquired, localized, macular, light brown to hyperpigmented lesion of the skin. Male-to-female ratio is 5:1. It occurs in adolescence. These lesions are usually localized on the shoulder, anterior chest or upper arms, but lesions in other areas have been repoed. Lesional tissue in Becker's naevus has been found to have an increased level of androgen receptors. [ Becker's nevus is present over the breast, ipsilateral breast hypoplasia may occur because of increased androgen receptors in the lesion and can cause asymmetric disfiguring. Iadvl textbook of dermatology page 175