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Seborrheic keratosis Benign neoplasms Growth factors Jeffrey J. Meffert, MD, 19626 Encino Knoll, San Antonio, TX 78259 (USA) Seborrheic keratoses (SKs) are among the most common benign cutaneous neoplasms. Despite this, knowledge of the pathophysiol-ogy underlying SKs is incomplete. Much of what is known about the growth and biology of SKs is obtained indirectly while investigating ‘more important’ tumors, and SKs are studied as ‘control neoplasms’. Ho and McLean [1] note that a true understanding of what makes SKs grow the way they do would help explain much about keratinocytes in general and the biology of the skin. We present what may be the first reported case of a naturally occurring ring-shaped SK, an entity which raises provocative questions about the growth factor milieu responsible for SKs. Case Report A 35-year-old man presented with an asymptomatic brown ring on his left arm which he had first noticed about 1 year previously (fig. 1). He was unsure if the lesion appaeared de novo as a 1 cm ring or if it had started as a solid papule and spread with central clearing. He denied any prior trauma or treatment such as cryotherapy, curet-tage, intralesional injections or topical wart therapies of any kind. Epi-luminescent biomicroscopy revealed sharp borders to the ring, scattered tiny ( < 1 mm) milia, a few small comedo-like openings and the absence of a melanocytic pigment pattern. A punch biopsy revealed acanthosis, papillomatosis and a rare keratin pearl. Although the epidermis was slightly effaced in the center of the ring, there was no fibrosis or other indication of a scar from prior trauma. The patient. The views expressed in this article are those of the authors and do not reflect the official policy of the Department of Defense or other Departments of the US Government. Fig. 1. Ring SK (1 cm diameter). weary of inquiries from friends and family about his ‘ringworm’, desired treatment and liquid nitrogen cryotherapy to the ring was performed. He presented several months later with a small residual arc-shaped ridge which was successfully treated with a second course of cryotherapy which eliminated the lesion. Discussion Many inflammatory conditions (e.g. granuloma annulare, gyrate erythemas, porokeratoses) are characterized by annular growth where the most histopathologically diagnostic areas of the lesion are found at the periphery of the ring rather than the often regressed or histologi-cally nonspecific center. While neoplasms may exhibit centrifugal growth, a perfect ring is a rarity.