A 55-year-old man with a 30-year history of occupational arsenic exposure presents with multiple hyperkeratotic papules on the palms and soles, along with a 2 cm indurated nodule on the dorsum of the right hand with irregular borders and central ulceration. Dermoscopy shows a vascular pattern with arborizing vessels. Histopathology reveals infiltrative nests of atypical keratinocytes with perineural invasion. Which of the following is the most likely diagnosis?

Explanation

## Diagnosis: Squamous Cell Carcinoma from Arsenical Keratosis ### Clinical Presentation Analysis The patient presents with classic features of malignant transformation of arsenical keratosis: **Key Point:** Chronic arsenic exposure is a well-established risk factor for development of cutaneous malignancies, particularly squamous cell carcinoma (SCC), basal cell carcinoma, and internal malignancies (lung, bladder). ### Diagnostic Features Supporting SCC from Arsenical Keratosis | Feature | Significance | |---------|-------------| | **Occupational arsenic exposure (30 years)** | Establishes carcinogen exposure; latency typically 10–40 years | | **Multiple hyperkeratotic papules on palms/soles** | Pathognomonic for arsenical keratosis (Bowen-like lesions) | | **2 cm indurated nodule with irregular borders** | Suggests invasive malignancy, not benign keratosis | | **Central ulceration** | Indicates tissue necrosis; common in SCC | | **Arborizing vessels on dermoscopy** | Characteristic of SCC (dilated, branching capillaries) | | **Infiltrative nests + perineural invasion on histology** | Hallmark of aggressive SCC; perineural invasion is a poor prognostic sign | **High-Yield:** Perineural invasion in SCC is associated with: - Higher recurrence rates - Increased risk of metastasis - Worse prognosis - Recommendation for Mohs micrographic surgery or wide excision with margin assessment ### Pathogenesis of Arsenic-Induced SCC 1. Chronic arsenic exposure → oxidative stress and DNA damage 2. Development of multiple arsenical keratoses (precancerous lesions) 3. Malignant transformation to SCC (occurs in ~5–10% of arsenical keratoses) 4. Invasive growth with perineural spread **Clinical Pearl:** Patients with arsenical keratosis should be monitored for: - Any change in size, color, or texture - Development of induration or ulceration - Systemic symptoms (weight loss, lymphadenopathy) suggesting metastasis - Internal malignancies (lung, bladder, kidney cancer) ### Why Perineural Invasion Matters ```mermaid flowchart TD A[SCC with Perineural Invasion]:::outcome --> B{Tumor spread pattern}:::decision B -->|Along nerves| C[Skip lesions possible]:::action B -->|Subclinical extension| D[Wider margins needed]:::action C --> E[Higher recurrence risk]:::urgent D --> F[Mohs surgery preferred]:::action E --> G[Metastatic potential]:::urgent ``` **Mnemonic: ARSENIC SKIN CANCER** — **A**rsenical keratosis, **R**ecurrent lesions, **S**quamous cell carcinoma, **E**xposure history, **N**eeds surveillance, **I**nvasive growth, **C**arcinogenic metal, **S**kin monitoring, **K**eratotic papules, **I**ncreased risk, **N**eoplastic transformation, **C**linical vigilance, **A**ggressive behavior, **N**eeds wide excision, **C**arcinoma risk, **E**arly detection, **R**ecurrence prevention **Tip:** In NEET PG exams, when you see "occupational arsenic exposure + hyperkeratotic papules + nodule with ulceration + perineural invasion," the answer is almost always **SCC from arsenical keratosis**. The perineural invasion is the key histologic finding that elevates this from simple SCC to a more aggressive variant requiring aggressive treatment. ### Treatment Considerations - **Mohs micrographic surgery** is the gold standard for SCC with perineural invasion - Wide local excision (5–10 mm margins) if Mohs unavailable - Consider sentinel lymph node biopsy if high-risk features present - Adjuvant radiotherapy if margins positive or extensive perineural invasion - Systemic surveillance for internal malignancies (chest X-ray, urinalysis, renal ultrasound) --- ## Why Other Options Are Incorrect **Option 1 (Basal Cell Carcinoma):** While BCC can also arise from arsenic exposure and may show perineural invasion, it typically presents as a pearly nodule with rolled edges and telangiectasia—not as a hyperkeratotic lesion on palms/soles. The clinical context of arsenical keratosis strongly favors SCC transformation. Additionally, the arborizing vessels on dermoscopy are more typical of SCC than BCC. **Option 2 (Merkel Cell Carcinoma):** MCC is a neuroendocrine carcinoma associated with Merkel cell polyomavirus, not arsenic exposure. It typically presents as a rapidly growing, painless nodule in sun-exposed areas (face, neck, extremities) in elderly patients. Histology would show small round blue cells with neuroendocrine differentiation (chromogranin, synaptophysin positive), not keratinocyte nests. The clinical presentation and exposure history do not fit. **Option 3 (Cutaneous Lymphoma):** Cutaneous T-cell lymphomas (mycosis fungoides) present with patches, plaques, or tumors, typically with pruritus and a history of progressive skin involvement. Histology shows atypical lymphocytes infiltrating the epidermis (epidermotropism), not keratinocyte nests. The occupational arsenic exposure and hyperkeratotic papules are not typical for lymphoma. Additionally, perineural invasion is not a feature of cutaneous lymphoma.