Irregular Streaks — SCE Dermatology MCQ

Correct answer: C — Radial growth phase melanoma — asymmetric peripheral streaks represent melanoma cells extending outward at the dermoepidermal junction, indicating active tumour growth at one edge

The correct answer is C, radial growth phase melanoma, where asymmetric peripheral streaks represent melanoma cells extending outward at the dermoepidermal junction, indicating active tumour growth at one edge. Streaks (radial streaming and pseudopods) are linear or bulb-ended pigmented projections at the lesion margin that histologically correspond to confluent junctional melanocytic nests advancing beyond the main tumour body. When these are distributed focally and asymmetrically, rather than symmetrically around the whole circumference, this reflects the radial growth phase of melanoma, where the tumour is spreading laterally at one edge rather than uniformly. This asymmetry is a recognised major dermoscopic criterion prompting urgent excision biopsy of the lesion under the two-week-wait suspected skin cancer pathway. Why the other options are wrong: E. Seborrhoeic keratosis: shows dermoscopic features such as milia-like cysts, comedo-like openings and a "moth-eaten" border, not peripheral pigmented streaks. D. Dermatofibroma: typically shows a central white patch (scar-like area) with a peripheral delicate pigment network, not radial streaming or pseudopods. B. Benign naevus growth: symmetrical radial streaming around the entire circumference (a "starburst" pattern) is characteristic of a benign Reed or Spitz naevus, not asymmetric focal streaks. A. Normal skin: shows no melanocytic structures at all, so streaks would not be a relevant finding. Key point: asymmetric, focal peripheral streaks (radial streaming or pseudopods) signal active radial growth phase melanoma and warrant excision, whereas symmetric circumferential streaks are typical of a benign Spitz/Reed naevus.

Reference: Dermoscopedia, Streaks (Radial streaming and pseudopods), https://dermoscopedia.org/Streaks