What are the clinical manifestations of skin cancer in the nailbed?

Clinical Manifestations of Skin Cancer in the Nailbed

Skin cancer in the nailbed most commonly presents as squamous cell carcinoma (SCC) with hyperkeratotic, warty proliferations, nail fold erosions, periungual swelling, paronychia, or ulceration of the lateral nail groove, while melanoma typically appears as longitudinal melanonychia (a brown-black streak) with irregular borders, color variegation, and possible Hutchinson sign (pigment spreading onto surrounding skin). 1

Squamous Cell Carcinoma Presentations

Common Clinical Features

• Hyperkeratotic, papillomatous or warty proliferations on any part of the nail unit or periungual tissue 1
• Erosions or scaling of the nail fold with whitish cuticle appearance 1
• Periungual swelling and paronychia with fissure or ulceration of the lateral nail groove 1
• Granulation-like tissue beneath with scabbing at the lateral nail groove 1

Nail Bed Involvement

• Subungual involvement is the most common presentation of SCC in the nail unit 1
• Onycholysis (nail plate separation from nail bed) with extensive hyperkeratosis of the nail bed 1
• Dystrophic or ingrown nail bed changes 1
• Longitudinal melanonychia has been reported as a presenting feature of SCC in situ, though this is less typical 1

Warning Signs of Invasive Transformation

The presence of ulceration, bleeding, or a nodule indicates transformation from in situ to invasive carcinoma. 1 When invasive malignancy develops, the metastasis rate is approximately 2%, though diagnosis is often delayed due to initial misdiagnosis as benign lesions. 1

Melanoma Presentations

Longitudinal Melanonychia Characteristics

• Tan, brown, or black longitudinal streak running from the proximal nail fold to the distal nail plate 2
• Bandwidth greater than 3 mm suggests malignancy 2
• Irregular borders that are blurry laterally rather than sharp 2
• Pigment variegation with haphazard combination of colors ranging from dark brown to black 2, 3

High-Risk Features (Hutchinson Sign and Beyond)

Periungual spread of pigmentation onto the adjacent cuticle and/or proximal and/or lateral nail folds (Hutchinson sign) strongly suggests melanoma. 2, 4 Additional concerning features include:

• Abrupt onset after middle age (melanoma is very rare in children) 2, 4
• Rapid growth or darkening of a melanonychia band 2, 3
• Proximal widening of the pigmented band 2
• Single digit involvement rather than multiple digits 2
• Associated nail plate dystrophy 2, 4
• Irregular elevation of the nail surface 2
• Bleeding mass in advanced cases 4

Diffuse Melanosis Pattern

A rapidly growing pigmented nail streak resulting in diffuse melanosis of the entire nail represents a possible early stage of subungual melanoma in situ. 3 This pattern shows many fine, dark longitudinal lines within diffuse, light-brownish pigmentation. 3

Critical Diagnostic Pitfalls

Delayed Diagnosis

Diagnosis of nail unit malignancies tends to be significantly delayed because of initial misdiagnosis as benign lesions or delay in performing biopsy. 1 The threshold for repeat biopsy should be low if the condition persists. 1

Histopathological Challenges

Biopsies can be open to misinterpretation, and distinguishing SCC in situ from invasive SCC may be difficult with periungual lesions due to the three-dimensional nature of the nail bed. 1 Therefore, biopsy specimens indicating SCC in situ should be treated as if there is a concurrent invasive component. 1

Biopsy Requirements

The nail plate must be sufficiently removed to expose the underlying lesion, and the nail matrix must be sampled by a practitioner skilled in nail apparatus biopsy. 5 Excisional biopsy is preferred when feasible, encompassing the entire lesion, while incisional biopsy is acceptable for larger lesions but must include adequate sampling of the nail matrix. 5

Distinguishing Benign from Malignant Pigmentation

Benign Patterns

• Exogenous pigmentations (bacterial, fungal, tar, blood) are usually not streaky or do not present as a stripe of even width with regular borders 6, 4
• Bacterial pigmentation (Pseudomonas, Proteus) has a greenish or grayish hue, often confined to the lateral nail edge 4
• Subungual hematoma from trauma is usually oval-shaped and does not form a neat streak 4

When to Observe vs. Biopsy

In children, most melanonychia is benign, and a wait-and-see approach is advocated. 2, 6 However, prolonged follow-up is mandatory for early detection of possible malignant changes. 2 Personal or family history of melanoma significantly increases suspicion for malignancy. 2