Melanoma questions love to hide in plain sight: a “weird mole,” a changing lesion, or a patient who finally noticed something “off.” The good news is you can catch most test stems (and real-life red flags) fast with one tight screen: ABCDE.
The Melanoma Mnemonic: ABCDE
Think: “A B C D E = Alarm Bells Catch Dangerous Evolving moles.”
Quick-hit table (memorize this)
| Letter | What it stands for | One-liner (USMLE-style) | What you should do |
|---|---|---|---|
| A | Asymmetry | One half doesn’t match the other → not a “normal” nevus look | Biopsy if suspicious |
| B | Border irregularity | Ragged, notched, poorly defined edges suggest malignant growth | Biopsy (don’t “watch and wait”) |
| C | Color variation | Multiple colors (tan, brown, black, red, blue, white) = concerning | Biopsy |
| D | Diameter | Classically > 6 mm (“bigger than a pencil eraser”)—but smaller can still be melanoma | Size supports suspicion; don’t let small size falsely reassure |
| E | Evolution | Change over time (size, shape, color, symptoms like bleeding/itching) is often the biggest clue | Most important red flag → biopsy |
A shareable visual: “Draw it in your head”
Picture a bad coin:
- A: Not a perfect circle—more like a lopsided blob
- B: Edges look like a coastline, not smooth
- C: Looks like it was spilled with different inks
- D: Bigger than an eraser
- E: It’s changing—like a photo “before vs after”
If a lesion makes you think “bad coin,” your next thought is: biopsy.
High-yield USMLE facts you’ll actually use
1) Best next step when melanoma is suspected
- Do an excisional biopsy (full-thickness) with narrow margins when feasible.
- Avoid shaving a clearly suspicious pigmented lesion if it risks inadequate depth assessment.
Why: Depth matters (staging/prognosis). Which brings us to…
2) Prognosis is about depth, not diameter
- Breslow depth (tumor thickness in mm) is the key prognostic factor.
- Deeper invasion = worse prognosis.
3) Risk factors worth recognizing in stems
- Intermittent intense UV exposure (blistering sunburns), especially childhood
- Fair skin, light eyes/hair, freckling
- Many nevi or dysplastic nevi
- Family history (e.g., CDKN2A mutations in some familial cases)
- Immunosuppression (transplant, HIV)
- Xeroderma pigmentosum (defective nucleotide excision repair → UV damage)
4) Melanoma subtype pearls (common Step associations)
- Superficial spreading melanoma: most common; radial growth; variegated color/shape
- Nodular melanoma: vertical growth early → worse; can be uniformly dark and rapidly growing
- Lentigo maligna melanoma: sun-damaged elderly (face); slow radial growth
- Acral lentiginous melanoma: palms/soles, under nails; more common in darker skin (but can occur in anyone)
5) Nail clue you should never ignore
- Subungual melanoma can present as a pigmented streak.
- Hutchinson sign: pigment extends onto the proximal/lateral nail fold → concerning.
6) Metastasis + clinical tie-in
- Melanoma can metastasize widely (skin, lymph nodes, liver, brain).
- Sentinel lymph node biopsy is used for staging in appropriate lesions.
Test-day pattern recognition: what the stem is trying to make you do
If the question shows a “changing mole” with ABCDE features → pick biopsy.
Not topical steroids. Not reassurance. Not “schedule follow-up in 6 months.”
Mini–rapid-fire examples
- “Asymmetric mole with irregular borders and multiple colors” → Excisional biopsy
- “New pigmented lesion on sole of foot” → Think acral lentiginous → biopsy
- “Dark streak in nail + pigment on nail fold” → Hutchinson sign → biopsy
The 10-second takeaway
ABCDE is your melanoma checklist, and E (Evolution) is the loudest alarm. When in doubt, biopsy early—because prognosis tracks with Breslow depth.