Visual recognition of cancers

Overview

Visual pattern recognition, supported by dermoscopy, underpins clinical diagnosis of the three major skin cancer types (basal cell carcinoma, squamous cell carcinoma, melanoma) - each with characteristic macroscopic and dermoscopic features that guide the decision to biopsy
Skin cancer is the most common cancer type in many populations with high UV exposure, making confident visual recognition a core clinical skill for early detection across primary care and dermatology

Basal cell carcinoma: pearly/translucent papule or nodule with rolled, telangiectatic border, may ulcerate centrally ("rodent ulcer") - arises from basal keratinocytes, slow-growing, essentially never metastasises
Squamous cell carcinoma: scaly, indurated, often tender nodule or plaque, may ulcerate - arises from atypical keratinocytes, faster-growing than BCC with a genuine (though generally low) metastatic potential
Melanoma: pigmented lesion assessed by the ABCDE criteria (Asymmetry, Border irregularity, Colour variegation, Diameter >6mm, Evolution/change) - arises from atypical melanocytes, the most dangerous of the three given its metastatic potential

ABCDE criteria structure macroscopic melanoma assessment; dermoscopy substantially improves diagnostic accuracy beyond the naked eye for all three cancer types (e.g. distinguishing pigmented BCC from melanoma, revealing arborising telangiectasia characteristic of BCC)
Any lesion that is new, changing, or does not fit the patient's other naevi ("ugly duckling" sign) warrants biopsy regardless of whether it strictly meets ABCDE criteria - change over time is itself a strong diagnostic signal independent of static appearance

Diagnostic uncertainty after clinical/dermoscopic assessment -> biopsy (excisional biopsy preferred for suspected melanoma, to allow accurate Breslow thickness measurement without the sampling error risk of partial/shave biopsy)
Confirmed diagnosis directs definitive treatment (excision with margins matched to cancer type and, for melanoma, Breslow thickness)

Basal cell carcinoma (most common, essentially non-metastasising), squamous cell carcinoma (intermediate metastatic risk), melanoma (highest metastatic risk, ABCDE assessment), dermoscopy (accuracy-enhancing adjunct to naked-eye examination)

The "ugly duckling" sign (a lesion that looks different from a patient's other naevi) and documented change over time are powerful diagnostic signals independent of whether a lesion strictly meets formal ABCDE criteria - over-reliance on ABCDE alone can miss an atypical-but-still-malignant lesion that doesn't fit the classic pattern

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