A 68-year-old farmer presents with a pearly, translucent nodule on his nose with visible telangiectasiasDilated superficial blood vessels visible on the skin surface. Classic for BCC because the tumor grows slowly and recruits new blood supply.. What's the most likely diagnosis?
Squamous cell carcinoma
Basal cell carcinoma
Melanoma
Actinic keratosis
Yes. Pearly + rolled borders + telangiectasias = BCC until proven otherwise. It's the most common skin cancer AND the most common cancer period. The "pearly" look comes from nests of basaloid cells with a palisading pattern that reflects light.
Good instinct, but pearly and translucent is BCC's signature look. SCC would be scaly and keratotic. Melanoma would be asymmetric and pigmented. Actinic keratosis is pre-malignant, not a nodule.
The Big Three
Boards will hand you a skin lesion and expect you to know which cancer it is in under 30 seconds. Here's the cheat sheet your brain actually needs:
Basal Cell Carcinoma
Frequency: Most common (80%)
Look: Pearly, waxy, rolled borders
Behavior: Locally invasive, almost never metastasizes
Cell: Basal layer of epidermis
Risk: UV + fair skin
Path: Palisading nuclei
Squamous Cell Carcinoma
Frequency: Second most common
Look: Scaly, crusty, ulcerated plaque
Behavior: Can metastasize (lip, ear higher risk)
Cell: Keratinocytes (squamous layer)
Risk: UV, immunosuppression, arsenic
Path: Keratin pearls
Melanoma
Frequency: Least common but most deadly
Look: Asymmetric, irregular borders, color variation
Behavior: Aggressive metastasis
Cell: Melanocytes (neural crest)
Risk: UV + dysplastic nevi + family hx
Path: S-100, HMB-45, Melan-A positive
The One Thing That Separates Each
BCC: Pearly. That's it. If the stem says pearly, translucent, waxy, or rolled borders — it's BCC. Nothing else looks like that. The tumor is made of basaloid cells that form little nests with palisading nucleiThe outer row of cells in BCC nests line up like a picket fence. This organized border is pathognomonic. It's why the lesion looks "pearly" — those orderly cells reflect light uniformly. at the edges, which is why it has that characteristic sheen.
SCC: Scaly and crusty. If the stem describes a rough, keratotic, ulcerated lesion — especially on sun-exposed skin — it's SCC. The key pathology buzzword is keratin pearlsConcentric whorls of keratin produced by malignant squamous cells. They look like little onion-ring cross-sections on histology. The more differentiated the tumor, the more pearls you see.. And remember: SCC can arise from actinic keratosisPrecancerous lesion from chronic UV damage. Rough, sandpaper-like patches. ~1-10% progress to SCC. Treat with cryotherapy or 5-FU cream. If it becomes tender or grows rapidly, biopsy it. — that's the precursor boards loves to test.
Melanoma: The ABCDEs. Asymmetry, Border irregularity, Color variation (multiple shades), Diameter > 6mm, Evolution (changing). If ANY of those are present in the stem, melanoma jumps to the top. Prognosis is all about Breslow depthMeasured in mm from the granular layer to the deepest point of invasion. THE single most important prognostic factor. <1mm = excellent. >4mm = poor. This is why early detection matters so much — depth at diagnosis determines survival. — deeper = worse.
Side-by-Side
| Feature |
BCC |
SCC |
Melanoma |
| Appearance |
Pearly, waxy nodule |
Scaly, ulcerated plaque |
Asymmetric pigmented lesion |
| Location |
Face (especially nose) |
Hands, face, lips, ears |
Anywhere (back in men, legs in women) |
| Precursor |
None (de novo) |
Actinic keratosis |
Dysplastic nevus |
| Metastasis |
Almost never |
Can (2-5%) |
Aggressive |
| Mortality |
Very low |
Low-moderate |
Highest of all skin cancers |
| Histology |
Palisading nuclei |
Keratin pearls |
S-100+, HMB-45+ |
| Treatment |
Mohs surgery, excision |
Excision, Mohs for high-risk |
Wide excision (margins by depth) |
| Genetics |
PTCH1 (Hedgehog) |
p53 mutation |
BRAF (V600E) |
Memory Hooks
BCC = "Beautiful Pearly Cancer"
It's the prettiest cancer you'll ever see. Smooth, shiny, translucent — like a pearl sitting on the skin. It's also the nicest — barely ever metastasizes. The beautiful one that doesn't leave.
SCC = "Scaly Crusty Cancer"
The name literally tells you what it looks like. Squamous = scaly. It even makes keratin pearls on histology — the cells are SO committed to being scaly that they form little keratin balls. Actinic keratosis is the warm-up act.
Melanoma = "The one that actually kills you"
Least common of the three. Most deadly by far. ABCDE is the screening tool. Breslow depth is the prognostic tool. If the stem says "changing mole" — that's the E (Evolution) and it's melanoma until proven otherwise.
PTCH1, p53, BRAF — "Patch the 53 BRAves"
BCC = PTCH1 (Hedgehog pathway — "patched"). SCC = p53 (the tumor suppressor everyone already knows). Melanoma = BRAF V600E (targeted by vemurafenib). In order of severity: Patch (minor) → p53 (moderate) → BRAF (aggressive).
Test Day Decision Tree
A lesion walks into your exam. Work through it:
Step 1: Is it pigmented with irregular features (asymmetry, color variation, evolving)?
Yes — pigmented, irregular, changing
No — not particularly pigmented or changing
Think MELANOMA. Biopsy immediately. Check Breslow depth. Stage it. ABCDE positive = melanoma until proven otherwise. Don't wait.
Step 2: Is it pearly, waxy, or translucent with telangiectasias?
Yes — pearly, shiny, rolled borders
No — rough, scaly, or ulcerated
Think BCC. Most common skin cancer. Locally destructive but almost never metastasizes. Mohs surgery for face/high-risk areas, excision otherwise. Check for Gorlin syndrome if young or multiple BCCs.
Step 3: Is it scaly, keratotic, or ulcerated on sun-exposed skin?
Yes — scaly, crusty, may be tender
No — doesn't match any of these
Think SCC. Second most common. CAN metastasize — especially lip, ear, immunosuppressed patients. Look for keratin pearls on biopsy. Ask about actinic keratosis history. Check for Marjolin ulcer if arising from a chronic wound/scar.
Consider other diagnoses: Merkel cell carcinoma (rapidly growing, violaceous nodule, immunosuppressed), dermatofibrosarcoma protuberans (slow-growing plaque), Kaposi sarcoma (violaceous patches/plaques, HHV-8). Biopsy everything suspicious.
Board Traps & High-Yield Associations
A patient with multiple BCCs at a young age, jaw cysts, and calcified falx cerebri. What syndrome?
Li-Fraumeni syndrome
Gorlin syndrome (Basal Cell Nevus syndrome)
Xeroderma pigmentosum
Familial atypical mole-melanoma syndrome
Gorlin syndrome = PTCH1 mutation (Hedgehog pathway). The triad boards tests: multiple BCCs + odontogenic keratocysts (jaw cysts) + calcified falx cerebri. Also get medulloblastomas. Autosomal dominant.
Multiple BCCs at a young age = Gorlin syndrome (PTCH1). Li-Fraumeni is p53 (sarcomas, breast, brain, adrenal). XP is nucleotide excision repair defect (all UV-related cancers). FAMM is melanoma risk (CDKN2A/p16).
Xeroderma pigmentosum (XP): Defective nucleotide excision repairNER fixes UV-induced thymine dimers. Without it, EVERY UV mutation accumulates. XP patients get all three skin cancers at extremely young ages. Autosomal recessive. They must avoid all sun exposure.. These patients get BCC, SCC, AND melanoma — all of them, because they can't fix ANY UV damage. Board question = child with severe sunburns → skin cancers.
Marjolin ulcer: SCC arising in a chronic wound or burn scar. The question stem will describe a non-healing ulcer in an old burn that suddenly changes. It's aggressive SCC in damaged tissue.
Immunosuppression → SCC: Transplant patients on immunosuppressants get SCC at massively increased rates (65-250x). Unlike the general population where BCC > SCC, in immunosuppressed patients SCC > BCC. This reversal is a board favorite.
Melanoma subtypes boards tests:
- Superficial spreading — most common overall (70%)
- Nodular — worst prognosis (grows vertically fast)
- Lentigo maligna — elderly, sun-damaged face, best prognosis
- Acral lentiginous — palms/soles/nails, most common in dark-skinned patients
Elimination Game
5 patients just walked in with skin lesions. Don't miss the diagnosis.
Quiz
4 of these from a pool of 14. Different every time. Let's go.