Seborrheic Keratosis Mimicking Basal Cell Carcinoma Under Dermoscopy: A Case Study
Did you know one of the most common benign skin growths—seborrheic keratosis (SK)—can sometimes look identical to a dangerous skin cancer under a dermoscope? A 2020 case study from dermatologists at Huazhong University of Science and Technology’s Union Hospital in Wuhan, China, reveals how tricky these diagnoses can be—even for experts using advanced diagnostic tools.
The Case: A Benign Growth That Looked Like Cancer
The patient was a 49-year-old woman with a 2-year history of a slow-growing, itchy brown papule on her right arm. The 4mm × 5mm lesion was rough, slightly hard, and had a central erosion (likely from scratching, she told doctors). When the team used dermoscopy—a handheld tool that magnifies skin to see fine details—they saw red flags for pigmented basal cell carcinoma (BCC): what looked like an ulcer, central “hairpin” blood vessels, blue-gray globules, and “leaf-like” edges (classic signs of BCC tumor nests).
But when they did a biopsy (taking a small skin sample for lab analysis), the results surprised them. The growth wasn’t BCC—it was an adenoid seborrheic keratosis, a less common type of SK where cells grow in tiny, gland-like strands from the epidermis into the dermis. The histopathology (tissue study) showed pseudohorn cysts (tiny keratin-filled pockets), epidermal hyperpigmentation, and inflammation from scratching—none of which are BCC features.
Why the Mix-Up? Atypical Features and Scratching
SK is usually easy to spot on dermoscopy: classic signs include comedo-like openings (blackheads), a “cerebriform” (brain-like) pattern, or milia-like cysts (tiny white bumps). But this adenoid SK had none of those. Worse, the patient’s scratching had changed the lesion’s appearance—making the central erosion look like an ulcer (hard to tell apart under dermoscopy) and altering the vessel patterns.
Key clues the team missed at first:
- Hairpin vs. arborizing vessels: BCC typically has “arborizing” (tree-like) vessels with white halos. This SK had hairpin vessels without halos—a sign of benign growths, per a 2017 study in J Dermatol.
- Erosion, not ulcer: The patient’s scratching caused surface damage (erosion), not deeper tissue loss (ulcer)—but dermoscopy can’t always tell the difference.
- Pigment mix-up: The blue-gray globules and leaf-like edges? They were actually hyperpigmentation (darkened skin cells) and free pigment in the dermis—mistaken for BCC’s tumor nests.
The Takeaway: Don’t Rely on One Tool
Dermoscopy is a game-changer for skin cancer diagnosis—but it’s not perfect. As the researchers note, atypical SK (especially the adenoid type) + trauma (like scratching) can mimic BCC. To get it right, doctors need to:
- Ask about symptoms (itchiness, scratching, changes).
- Use clinical exams and dermoscopy.
- Do a biopsy if features are unclear.
What This Means for You
If you have a skin growth that’s:
- Changing shape/size/color
- Itchy, bleeding, or sore
- Atypical (no “classic” SK features like waxy texture)
Don’t self-diagnose. See a dermatologist. They’ll combine dermoscopy, your medical history, and (if needed) a biopsy to rule out cancer—even if the growth looks “benign” at first glance.
Study Details
This case was published in the Chinese Medical Journal (2020) by Yao-Ying Gao, Xiang-Jie An, Jing Yang, Chang-Zheng Huang, and Juan Tao (Department of Dermatology, Union Hospital, Tongji Medical College). The full study is available via doi.org/10.1097/CM9.0000000000001010.
Previous research cited:
- J Eur Acad Dermatol Venereol (2014): Clonal SK dermoscopy.
- J Am Acad Dermatol (2019): Dermoscopy for skin neoplasms.
- J Dermatol (2017): Dermoscopy-pathology links in SK.
Remember: When it comes to skin health, “better safe than sorry” isn’t just a saying—it’s good medicine.
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