Tumors: Benign vs Malignant Differentiation

Introduction

The primary goal in tumor diagnostics is not to name the specific tumor immediately, but to categorize it as Benign, Suspicious, or Malignant.

This chapter provides the visual criteria to make that distinction.

12.1 Pigmented Lesion: Nevus vs Melanoma

"Ugly Duckling" Sign

In any given patient, benign nevi tend to look similar ("Signature Nevi").

Rule: The lesion that stands out—is darker, larger, or redder than the others—is the "Ugly Duckling" and requires biopsy.

ABCDE Criteria (Revised for Diagnosis)

A - Asymmetry:
- Benign: You can fold it in half and it matches.
- Malignant: One half is different in shape/color.
B - Border:
- Benign: Smooth, even.
- Malignant: Scalloped, notched, or "leaking" pigment.
C - Color:
- Benign: One or two shades of brown.
- Malignant: Red, White, and Blue (The danger colors). Jet black.
D - Diameter:
- Context: >6mm is the classic cutoff, but small melanomas exist.
E - Evolution:
- The most important sign. Any change in a mole after age 30 is suspicious.

12.2 "Black Tumor" Differential

When you see a black nodule, consider:

Diagnosis	Key Differentiating Feature	Test
Melanoma (Nodular)	History of Growth. Asymmetric.	Biopsy (Excisional)
Seborrheic Keratosis	"Stuck-on". Dull surface. Horn cysts.	Dermoscopy (Cysts)
Pigmented BCC	Pearly rolled border. Telangiectasia.	Dermoscopy (Maple leaf)
Thrombosed Angioma	Sudden onset. Painful. Red/Purple rim.	Dermoscopy (Lacunae)
Blue Nevus	Stable. Homogeneous Steel-Blue color.	History (Long standing)

12.3 "Pink Nodule" Differential

Amelanotic tumors are harder to diagnose.

Diagnosis	Signs
Basal Cell Carcinoma	Translucent/Pearly. Arborizing vessels. Central crushing/ulceration.
Squamous Cell Carcinoma	Keratotic (scaly/rough). Indurated (hard) base. Tender.
Amelanotic Melanoma	The "great masquerader". Look for Remnant Pigment at the edge. Vascular pattern is atypical (dotted/linear vessels).
Merkel Cell Carcinoma	AEIOU Rule: Asymptomatic, Expanding, Immune suppression, Older >50, UV exposed. Red-violet, hard nodule.

12.4 Specific Diagnostic Signs

"Dimple Sign" (Fitzpatrick)

Method: Lateral compression of a pigmented nodule.
Result: Depression (Dimple).
Diagnosis: Dermatofibroma (Benign).
Why: Fibrous tethering to subcutis.

"Barnacle" Sign

Appearance: Waxy, verrucous, "stuck-on" plaque.
Diagnosis: Seborrheic Keratosis.
Pearl: You can pick the edge with a fingernail (don't do this, but it looks like you can).

"Pearly" Sign

Appearance: Translucent, shiny quality to the rim of a papule.
Diagnosis: Basal Cell Carcinoma.
Note: Best seen with stretching the skin.

Hutchinson's Sign (Nail)

Appearance: Pigment extending from the nail plate onto the proximal nail fold (cuticle).
Diagnosis: Subungual Melanoma.
Mimic: Pseudo-Hutchinson (pigment visible through transparent cuticle).

12.5 Diagnostic Algorithm: Facial Papule

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