A 32-year-old woman presents to a dermatology clinic with multiple pigmented lesions on sun-exposed areas of her skin and a history of severe sunburns in childhood. Genetic testing reveals mutations in the XPA gene affecting nucleotide excision repair (NER). She is concerned about her cancer risk. What is the most appropriate immediate next step in management?

Explanation

## Clinical Context: Xeroderma Pigmentosum (XP) **Key Point:** XPA mutations cause defective nucleotide excision repair (NER), the primary pathway for removing UV-induced thymine dimers and bulky DNA adducts. Patients develop severe photosensitivity, pigmentary changes, and a 1000-fold increased risk of skin cancer (melanoma, basal cell carcinoma, squamous cell carcinoma) by age 40. ## DNA Repair Defect in XP **High-Yield:** The NER pathway has two sub-pathways: - **Global Genome Repair (GGR):** removes lesions from transcriptionally silent regions - **Transcription-Coupled Repair (TCR):** removes lesions from actively transcribed genes XPA protein is essential for both pathways; its loss means UV lesions persist, leading to mutations and malignant transformation. ## Management Strategy: Early Detection & Surveillance The most appropriate immediate action is **baseline total body skin examination with establishment of regular surveillance**. This achieves: 1. **Documentation of baseline lesion burden** — essential for tracking progression 2. **Early detection of malignant transformation** — melanomas detected at stage I have ~95% 5-year survival; stage IV <20% 3. **Patient education** — strict photoprotection (SPF 50+, protective clothing, UV-blocking windows) 4. **Dermatoscopy protocol** — 3-monthly intervals allow detection of new or changing lesions before invasive growth **Clinical Pearl:** Patients with XP require lifelong surveillance because new skin cancers can develop at any age. Surveillance is the only evidence-based intervention that improves outcomes; prophylactic excision and systemic retinoids lack robust evidence in XP. ## Why Other Options Fail | Option | Why Incorrect | |--------|---------------| | Topical 5-FU | Treats existing actinic keratosis but does not prevent new DNA damage or address the underlying repair defect; not first-line | | Oral retinoids | May reduce cancer incidence in high-risk patients but requires baseline labs, monitoring, and teratogenicity counseling; not the immediate next step before establishing surveillance | | Prophylactic excision | Mutilating and impractical; XP patients develop multiple new lesions over time; surveillance with selective excision of suspicious lesions is standard | **Mnemonic:** **SURVEILLANCE First** — **S**kin exam baseline, **U**V avoidance counseling, **R**egular dermoscopy, **V**igorous follow-up every 3 months, **E**arly excision of suspicious lesions.