Medicine (MD/DO)
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First Aid for the USMLE Step 1 (2023)
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Seborrheic Keratosis

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Seborrheic Keratosis

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Seborrheic Keratosis

Saber-fish Carrot-toes
Flat, Greasy, Pigmented Squamous Epithelium
Flat Square-mouse

Seborrheic keratosis is a benign tumor of the skin that is characterized by flat, greasy, pigmented squamous epithelium.

"Stuck-On" Appearance

This disorder presents with the appearance of being stuck on the skin's surface.

Horn Cysts
Horn Cyst-sisters

Seborrheic keratosis in histology can be seen with keratotic invaginations (“pseudo-horn cysts”) and intraepithelial keratin cysts (“true horn cysts”).

Proliferation of Immature Keratinocytes
Growing Baby Carrot-tin

Seborrheic keratosis occurs as a proliferation of immature keratinocytes. This mechanism is still not well understood, but it is thought to be related to the mutation of fibroblast growth factor receptor 3 (FGFR3) and/or PIK3CA oncogenes.

Most Common Benign Tumor in the Elderly
#1 Foam-finger Bunny Old-man

Seborrheic keratosis is the most common benign tumor in the elderly.

Head, Trunk, and Extremities
Head, Trunk, and Extremities

Seborrheic keratosis is commonly seen in the head, truck, and extremities.

GI Adenocarcinoma
GI Add (+) car-gnome

Due to its relation to certain malignancies, such as GI adenocarcinoma, multiple seborrheic keratoses that grow rapidly should raise concern. This condition is known as Leser-Trelat sign and is thought to occur due to the secretion of growth factors and cytokines from the malignancy neoplasm, which then triggers the eruptive growth of seborrheic keratosis.

Leser-Trelat Sign
Laser-Tree Sign

GI adenocarcinoma is the most common malignancy found in association with Leser-Trelat sign, followed by breast cancer and lymphoma. Other malignancies are mycosis fungoides, prostate, lung, nasopharyngeal carcinoma, squamous cell carcinoma, kidney, laryngeal, ovarian, hepatocellular carcinoma, melanoma, and bladder cancer.


This disorder often doesn't need treatment. However, we should know how to differentiate seborrheic keratosis from malignant skin tumors.

Mr. Cry-O

Treatment available for seborrheic keratosis is surgical or ablative, such as cryotherapy, curettage, shave removal, laser modalities, and chemical peels. Cryotherapy is the most common modality, which uses cold temperatures to damage lesions.


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