This is the answer and explanation for USMLE Question #19 from the Dr. Ray Makar Facebook page. Try it first, then check your answer below.
The Question
A biopsy of an irregular, multicolored pigmented lesion on the back confirms malignant melanoma. Which factor is most important for prognosis?
A. Breslow thickness (depth of invasion)
B. Diameter of the lesion
C. Number of colors in the lesion
D. Age of the patient
Correct Answer: A. Breslow thickness (depth of invasion)
The depth of invasion, measured in millimeters from the top of the granular layer to the deepest tumor cell, is the single most important prognostic factor in melanoma. Deeper tumors are more likely to have spread; depth also guides surgical margins and the decision to do a sentinel lymph node biopsy.
Why the Other Answers Are Wrong
- Diameter: a warning sign (D in ABCDE) for spotting suspicious moles, but not the main prognostic factor once melanoma is diagnosed.
- Number of colors: color variation helps you suspect melanoma, but does not predict outcome.
- Age of the patient: may affect outcome slightly, but is far less important than tumor depth.
High-Yield Pearl
Remember ABCDE for suspicious moles: Asymmetry, Border irregularity, Color variation, Diameter over 6 mm, Evolution (change). Melanoma is S-100 and HMB-45 positive; BRAF V600E mutations can be treated with vemurafenib.
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