Nail Squamous Cell Carcinoma
Squamous cell carcinoma of the nail unit (nail, periungual or subungual SCC) is the most common primary malignant tumor of the nail apparatus, accounting for more than 50–70% of all nail malignancies. It can arise from the nail folds (periungual), the nail bed (subungual) or the nail matrix.
Unlike ordinary skin SCC, which is driven by sun exposure, nail SCC is closely linked to high-risk human papillomavirus (HPV), especially HPV-16 (60–80% of cases), as well as HPV-18, 31, 35 and 56. Other contributing risk factors include ionizing radiation, chronic chemical exposure (arsenic), immunosuppression (HIV, organ transplantation) and repeated microtrauma.
- Histopathology:
- SCC in situ (Bowen's disease): Full-thickness loss of the normal layered architecture of the epidermis, with atypical proliferating keratinocytes, hyperchromatic nuclei, numerous atypical mitoses and premature keratinization (dyskeratosis), but an intact basement membrane.
- Invasive SCC: Nests and islands of atypical epithelial cells break through the basement membrane and invade deep into the dermis and nail bed stroma, with numerous keratin pearls, reactive stromal fibrosis (desmoplasia) and a chronic inflammatory infiltrate.
- Immunohistochemistry (IHC):
- HPV-associated SCC shows strong, diffuse p16INK4a staining (a surrogate marker for high-risk HPV) and is positive for cytokeratin 5/6, p63 and p40.
- How the Tumor Destroys the Nail Plate and Invades Bone:
- Proliferating malignant cells destroy the nail matrix, causing the nail plate to lift (onycholysis), become warty and ulcerated, or lose its shape completely.
- As the tumor grows deeper, it breaches the periosteum and erodes the bone of the fingertip (distal phalanx erosion).
Because it can look like many benign conditions, nail SCC is most often misdiagnosed as periungual warts (verruca vulgaris), fungal nail infection (onychomycosis) or chronic paronychia. The average diagnostic delay is 4–8 years, so many patients develop bone invasion that could have been avoided. At Haute-Derma, targeted onychoscopy, biopsy with p16INK4a staining and Mohs micrographic surgery are the keys to preserving as much finger length as possible.
Clinical Features and Digital Onychoscopy Findings
Nail SCC progresses quietly and is usually painless early on (pain appears only once it invades bone or becomes infected). It most often affects the fingers, especially the thumb and index finger, in men aged 50–70.
Clinical Presentations
- Recurrent verrucous (wart-like) form: A rough, thickly keratotic growth around or under the nail that keeps coming back despite repeated laser or wart treatments.
- Ulcerative form: A shallow or deep ulcer in the nail bed with raised, friable edges that bleeds easily on contact and may ooze foul-smelling pus.
- Erythronychia / onycholysis form (longitudinal erythronychia): A red longitudinal band in the nail plate or slowly progressive localized nail lifting, with rough keratin building up at the free edge.
Digital Onychoscopy (Nail Dermoscopy) Findings
- Polymorphous vascular pattern: Several types of abnormal new vessels appear together: glomerular vessels, hairpin vessels and irregular, tortuous microvessels.
- Loss of the parallel capillary pattern: The normal longitudinal capillaries of the nail bed disappear completely and are replaced by rough white-yellowish keratotic areas.
Distinguishing Nail SCC from Look-Alike Conditions
| Squamous Cell Carcinoma (SCC) | Periungual Wart (Verruca) | Amelanotic Melanoma |
|---|---|---|
| Malignant squamous epithelial cancer | Benign HPV-induced growth | Malignant melanocytic cancer |
| Resistant to all standard treatments | Responds to laser, acids or cryotherapy | Does not respond to antifungals or antibiotics |
| Polymorphous vessels, thick keratotic scale | Black dots (thrombosed capillaries) | Linear or dotted vessels, faint pigment remnants |
| Bone erosion or defect (late) | Usually no bone erosion | Extensive destructive bone erosion |
| p16INK4a (+), p63 (+) | p16INK4a (–) or weak | S100 (+), SOX10 (+), Melan-A (+) |
Diagnosis, Mohs Surgery and Digit Preservation at Haute-Derma
At Haute-Derma, patients with long-standing warty or ulcerated lesions around the nail are managed with our digit-sparing Mohs surgery protocol (Haute-Derma Nail SCC Protocol):
Imaging and Confirmatory Biopsy
- Finger X-rays (AP and lateral): Assess any damage to the cortex of the distal phalanx.
- Confirmatory biopsy (incisional / punch biopsy): Taken through the nail plate to include the full thickness of the nail bed down to the periosteum. The specimen is stained with H&E and p16INK4a to confirm SCC and its HPV association.
Mohs Micrographic Surgery (MMS)
- Mohs surgery is the treatment of choice, offering a very high rate of complete tumor removal while preserving as much finger length and function as possible.
- The surgeon removes the tumor layer by layer, maps each piece and examines frozen sections under the microscope during the operation. This is repeated until all margins (peripheral and deep) are completely clear of cancer cells (margin-negative).
- If Mohs is not available: wide local excision (WLE) is performed with a 4–5 mm safety margin.
Managing Invasion of the Distal Phalanx
- If the periosteum and cortex are intact: The periosteum is cleared locally and the distal phalanx is fully preserved.
- If the distal phalanx is eroded or invaded (bone invasion): Amputation at the distal interphalangeal joint (DIP joint amputation) or partial amputation of the distal phalanx is required to ensure the cancer is fully removed.
Reconstruction and Functional Recovery
- Rotated local flaps or a full-thickness skin graft are used to cover the bone or soft tissue defect.
- An HPCH polymer film dressing and low-level light therapy (630 nm) help the wound heal faster and reduce scar contracture of the finger.
