Melanoma vs Seborrheic keratosis
How to tell Melanoma and Seborrheic keratosis apart when a board question makes them look alike.
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Evolution in size, shape, or color is the highest-yield discriminator favoring melanoma over seborrheic keratosis.
Side by side
Asymmetric pigmented lesion with color variation, irregular border, enlargement, or evolution suggests melanoma.
Well-circumscribed waxy stuck-on papule in older adults suggests seborrheic keratosis.
Melanoma arises from malignant melanocyte transformation with invasive and metastatic potential.
Seborrheic keratosis is a benign epidermal proliferation without malignant behavior.
Suspicious melanoma lesions require full-thickness excisional biopsy with narrow margins for Breslow depth staging; ulceration and mitotic activity inform prognosis.
Seborrheic keratosis is diagnosed clinically; dermoscopy may show milia-like cysts and comedo-like openings, and biopsy is done only when diagnosis is uncertain.
The trap
Dark waxy plaques can be falsely reassured as seborrheic keratosis, delaying diagnosis of melanoma. Any changing asymmetric lesion with variegated pigment should undergo excisional biopsy rather than destructive office treatment.
The repair move
Next best step: perform full-thickness excisional biopsy with 1 to 3 mm clinical margins for histologic diagnosis and Breslow depth assessment. If melanoma is confirmed, proceed with stage-appropriate wide local excision and consider sentinel lymph node biopsy when Breslow depth is 0.8 mm or greater or ulceration is present.
Try a free question
CoreA 68-year-old woman has a new pigmented lesion with asymmetry, irregular borders, and color variation from tan to black. BP 130/78 mm Hg, HR 74/min, temp 36.7 C. The lesion has grown from 4 mm to 11 mm in 5 months. What is the most likely diagnosis?
Show answer and explanation
Answer: B. Melanoma. Rapidly evolving asymmetric variegated pigmented lesion is most consistent with melanoma.
Why the other choices are tempting
- A. Seborrheic keratosis is usually waxy stuck-on and less evolution-prone in this malignant pattern.
- C. Dermatofibroma is typically firm and dimples on lateral compression.
- D. Solar lentigo is usually uniformly pigmented and stable.
- E. Basal cell carcinoma typically appears pearly with telangiectasias rather than pigmented ABCDE changes.
Flashcards
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Which ABCDE element most strongly implies malignant transformation over benign seborrheic keratosis?
Evolution, meaning recent change in lesion appearance, is one of the strongest melanoma warning signs.
What visual description is classic for seborrheic keratosis?
A waxy stuck-on papule or plaque with sharp borders is classic for seborrheic keratosis.
Quick answers
What is the fastest way to tell Melanoma from Seborrheic keratosis?
Evolution in size, shape, or color is the highest-yield discriminator favoring melanoma over seborrheic keratosis.
What is the key clue for Melanoma?
Asymmetric pigmented lesion with color variation, irregular border, enlargement, or evolution suggests melanoma.
What is the key clue for Seborrheic keratosis?
Well-circumscribed waxy stuck-on papule in older adults suggests seborrheic keratosis.
What is the common trap with Melanoma vs Seborrheic keratosis?
Dark waxy plaques can be falsely reassured as seborrheic keratosis, delaying diagnosis of melanoma. Any changing asymmetric lesion with variegated pigment should undergo excisional biopsy rather than destructive office treatment.