Random Dermatology MCQ - Invasive Squamous Cell Carcinoma

A 65-year-old farmer presents for evaluation of a lesion on his ear. He reports it started as a small, scaly spot years ago but has recently thickened, become tender, and bled on occasion. Examination reveals a 1.2 cm firm, erythematous, hyperkeratotic plaque with a central keratin-filled crater on the helix of the right ear. The surrounding skin shows significant solar damage. Which of the following is the most likely diagnosis?

A) Actinic keratosis
B) Keratoacanthoma
C) Nodular basal cell carcinoma
D) Cutaneous horn
E) Invasive squamous cell carcinoma

Correct Answer: E) Invasive squamous cell carcinoma

Explanation

This clinical presentation is highly characteristic of invasive squamous cell carcinoma (SCC) developing on a high-risk site (the ear) with a classic history of progression from a precursor lesion.

Key Clinical and Histopathological Correlation:

1. Clinical History:

   • Origin: The history of a long-standing "scaly spot" suggests a precursor actinic keratosis (AK).

   • Progression: The recent changes of thickening, tenderness, and bleeding are classic "red flags" indicating transformation from a pre-malignant AK to an invasive SCC. This progression represents the transformation from intraepidermal dysplasia to invasion through the basement membrane.

2. Examination Findings:

   • Location: The helix of the ear is a high-risk site for SCC due to chronic sun exposure.

   • Morphology: The description of a "firm, erythematous, hyperkeratotic plaque" is typical of SCC. The central keratin-filled crater is a highly characteristic feature, often representing a focus of abnormal keratinization (horn pearl) within the invasive tumor.

   • Background: "Significant solar damage" (solar elastosis) provides the etiological context.

Why Not the Other Options?

• (A) Actinic keratosis: An AK would present as a simpler, scaly papule or plaque without induration, a central crater, or bleeding. This lesion has progressed beyond an AK.

• (B) Keratoacanthoma (KA): A KA is now considered a variant of SCC. It classically presents as a rapidly growing, dome-shaped nodule with a central keratotic crater that may resolve spontaneously. However, the history here is of a slowly progressing lesion over years, not the rapid growth (weeks to months) typical of KA.

• (C) Nodular basal cell carcinoma: A BCC would typically present as a pearly papule with telangiectasia and a rolled border, often with central ulceration, but not typically with a prominent hyperkeratotic or crateriform surface.

• (D) Cutaneous horn: A cutaneous horn is a clinical description of a protruding column of keratin. The key is that SCC is found at the base of the horn in up to 20% of cases. This answer is a distractor; the horn is the keratin crater, but the diagnosis is the malignant cause of it—the invasive SCC.

Histopathological Correlation:
The biopsy of this lesion would be expected to show:

• Invasive strands and nests of atypical keratinocytes extending into the dermis.

• Keratin pearls (horn pearls) within the invasive tumor nests, correlating with the clinical "keratin-filled crater."

• Solar elastosis in the surrounding dermis.

• Likely areas of adjacent actinic keratosis (squamous cell carcinoma in situ).

Management:
Given the high-risk location, the definitive treatment would be surgical excision (e.g., Mohs micrographic surgery) to ensure complete removal and precise margin control.