12-phase flow (12)

1. 1FRAME
   Frame as a UV-driven keratinocyte dysplasia → carcinoma continuum on a field-cancerised canvas: AK (precursor with a measurable progression risk) → SCC in situ (Bowen) → invasive cSCC, alongside BCC (the most common human cancer — locally destructive, rarely metastatic). The dermatology engine owns recognition → biopsy → lesion-vs-field therapy → risk-stratified surgery → surveillance, and ROUTES advanced systemic disease to oncology by engine_id while co-managing checkpoint-inhibitor cutaneous toxicity. The failure modes are missing an invasive cSCC under an "AK", under-treating the field, and under-recognising the aggressive transplant cSCC (AAD 2018 BCC PMID 29331385 + cSCC PMID 29331386).
   advance: continuum + field-cancerisation framing set; advanced-systemic + melanoma + irAE routes noted by engine_id
2. 2ENTRY
   Recognise the continuum entry: rough sandpapery photodistributed AK field, a pearly telangiectatic rolled-border BCC, an indurated/ulcerated cSCC pivot lesion, or a high-risk surveillance/transplant entry; capture lesion morphology + dermoscopy up front (the core recognition signal — pigmented lesions route to derm.melanoma.core.v1).
   inputs: lesion_morphology_and_dermoscopy
   actions: workup.chronic_pruritus
   advance: entry trigger present; morphology + dermoscopy recorded; pigmented lesion routed out
3. 3CONTEXT
   Build the risk-conditioned context: cumulative photodamage + Fitzpatrick + age + outdoor/radiation/scar/voriconazole/HPV exposure, immunosuppression status (solid-organ transplant ≈ 65–100× cSCC and aggressive; CLL/HIV), prior-NMSC count/sites + AK burden (field cancerisation), and genetic photosensitive syndromes (Gorlin, xeroderma pigmentosum, albinism). These set the pre-test prior, the field-vs-lesion strategy and the surveillance cadence.
   inputs: photodamage_and_risk_factors, immunosuppression_status, prior_nmsc_count_and_sites, genetic_photosensitive_syndrome
   actions: workup.chronic_pruritus
   advance: risk-conditioned prior + field + immunosuppression + genetic context established
4. 4RED_FLAGS
   Do NOT field-treat or monitor an invasion-suspicious lesion — induration, tenderness, rapid growth, hyperkeratotic/ulcerated change, or failure of adequate field therapy is the AK-vs-invasive-cSCC biopsy pivot. Screen the not-to-miss: locally advanced / deeply fixed / perineural-symptomatic NMSC, regional nodal disease, and the aggressive new/recurrent NMSC in a transplant recipient (accelerated derm + transplant coordination). Checkpoint-inhibitor severe irAE in a patient on routed systemic therapy is an emergent route-out.
   inputs: invasion_features_induration_tenderness_growth_ulceration, locally_advanced_or_metastatic_signs
   actions: panel.cbc, panel.inflammation
   advance: invasion-suspicious lesion routed to urgent biopsy; locally-advanced/nodal/transplant/irAE red flags screened and escalated/routed if present
5. 5INITIAL_WORKUP
   DIAGNOSTIC BIOPSY for any lesion with invasion features or diagnostic uncertainty (shave adequate for most AK/superficial NMSC; punch/deeper biopsy when depth/invasion matters — empiric field therapy of an undiagnosed indurated nodule is NOT acceptable as it masks invasive cancer). Histopathology: BCC subtype (nodular/superficial vs aggressive infiltrative/morpheaform/micronodular/basosquamous), cSCC differentiation/depth/perineural invasion/lymphovascular invasion, in-situ vs invasive. Baseline CBC/LFT only if advanced systemic therapy is anticipated — routine bloods/imaging are NOT indicated for localised low-risk disease (AAD 2018 BCC PMID 29331385 + cSCC PMID 29331386).
   inputs: cbc_with_differential, lft
   actions: panel.cbc, panel.lft
   advance: definitive biopsy obtained with adequate technique; histologic subtype + invasion/perineural reported; baseline labs only if systemic anticipated
6. 6BRANCHING_WORKUP
   Histopath-driven branch: AK / SCC in situ → lesion- vs field-directed therapy; low-risk BCC/cSCC → excision/C&E/topical; high-risk cSCC (BWH/AJCC8 features) → Mohs + consider nodal imaging/SLNB discussion + MDT; aggressive-subtype/recurrent/H-zone BCC → Mohs; locally advanced/metastatic BCC or cSCC → cross-sectional staging imaging (CT/MRI for bone/orbit/perineural; nodal US/CT), and route advanced systemic therapy to oncology with carryover. Transplant recipients branch to accelerated surveillance + transplant-team immunosuppression-modulation coordination.
   inputs: high_risk_cscc_features, tumor_site_size_recurrence_status
   actions: workup.le_edema, panel.inflammation
   advance: AK-vs-low-risk-vs-high-risk-vs-advanced branch assigned; staging imaging + MDT ordered as indicated; transplant pathway flagged
7. 7DIFFERENTIAL
   Terminal lesion differential with named pivots: AK (rough strawberry-pattern macule) vs SCC in situ/Bowen (well-demarcated scaly plaque) vs invasive cSCC (indurated/tender/ulcerated — biopsy pivot) vs BCC (pearly, rolled border, arborising vessels — basal vs squamous) vs melanoma (pigmented → route derm.melanoma.core.v1) vs seborrheic keratosis (stuck-on, milia-like cysts) vs keratoacanthoma (rapid crateriform — cSCC variant, treat as cSCC) vs benign lichenoid keratosis vs amelanotic/hypertrophic mimics vs porokeratosis (raised keratotic rim) vs hypertrophic actinic vs psoriasis/eczema patch. Dermoscopy pivots: BCC arborising vessels / leaf-like / blue-grey ovoid nests / spoke-wheel; cSCC white circles / keratin / looped & hairpin vessels; AK red pseudonetwork / strawberry pattern.
   advance: single best diagnosis selected; keratoacanthoma treated as cSCC; pigmented routed to melanoma engine; in-situ vs invasive resolved
8. 8RISK_STRATIFICATION
   BCC: there is NO formal AJCC staging — stratify by recurrence risk (site/size/border definition/histologic subtype/recurrent/immunosuppression/prior RT). cSCC: NCCN low- vs high-risk + BWH (Brigham and Women’s) and AJCC8 high-risk staging (≥2 cm, >6 mm or beyond subcutaneous fat depth, perineural invasion ≥0.1 mm, poor differentiation, ear/lip/temple, recurrent, immunosuppression) — these are schema-blocked as TS calculators and captured narratively. The tier drives modality: low-risk → excision/C&E/topical; high-risk → Mohs/MDT + staging; locally advanced/metastatic → systemic routing.
   inputs: high_risk_cscc_features, tumor_site_size_recurrence_status
   actions: panel.inflammation
   advance: BCC recurrence-risk tier or cSCC low/high-risk (BWH/AJCC8) tier assigned; advanced-disease routing decided
9. 9TREATMENT
   AK/field: lesion-directed cryotherapy for discrete lesions; FIELD therapy (topical 5-fluorouracil, imiquimod, tirbanibulin, diclofenac, photodynamic therapy, 5-FU+calcipotriol immune-priming) for the cancerised field. Low-risk BCC/cSCC: surgical excision with margins or curettage & electrodesiccation; superficial-BCC topical imiquimod/5-FU; radiotherapy if non-surgical. High-risk / facial H-zone / recurrent / large / aggressive-histology: Mohs micrographic surgery (tissue-sparing, lowest recurrence). Locally advanced/metastatic BCC: Hedgehog inhibitor vismodegib or sonidegib; cemiplimab if Hedgehog-failed/intolerant. Locally advanced/metastatic cSCC: anti-PD-1 cemiplimab (first-line) or pembrolizumab + adjuvant RT for high-risk — ROUTED to oncology shared-care by engine_id. Chemoprevention: photoprotection, oral nicotinamide, acitretin for high-risk/transplant; transplant immunosuppression reduction/mTOR-switch coordinated with the transplant team. Gate: Hedgehog inhibitor absolute teratogen (pregnancy/contraception), checkpoint inhibitor allograft-rejection risk in solid-organ-transplant (multidisciplinary), 5-FU pregnancy/DPD, imiquimod inflammatory expectation; elderly/frail → non-surgical or watchful waiting for low-risk BCC.
   inputs: age, pregnancy_status, creatinine
   advance: lesion-vs-field plan or risk-stratified surgical modality set; chemoprevention + transplant-coordination defined; advanced systemic routed to oncology with carryover; agent gated on pregnancy/age/transplant
10. 10DISPOSITION
    Almost entirely outpatient: cryotherapy/field therapy/excision/C&E/Mohs as office or day procedures; surveillance in derm/onco-derm clinic. Multidisciplinary tumour-board referral for high-risk cSCC, locally advanced/metastatic disease, perineural invasion, or bone/orbit/parotid involvement; oncology shared-care for any advanced systemic therapy; urgent referral for fixed/symptomatic locally advanced disease. Transplant recipients are co-managed with the transplant team for immunosuppression modulation.
    inputs: locally_advanced_or_metastatic_signs
    advance: disposition documented; MDT/oncology referral made for high-risk/advanced disease; advanced systemic delegated by engine_id; transplant co-management arranged
11. 11MONITORING
    Post-treatment recurrence + new-primary surveillance at a risk-based cadence (AAD 2018: low-risk BCC/cSCC every 6–12 mo; high-risk cSCC every 3–6 mo for the first 2 years then extend; lifelong total-body skin exam). Transplant recipients intensified (every 3–6 mo, sometimes monthly with heavy burden). On routed advanced systemic therapy: Hedgehog inhibitor AEs (muscle spasm, dysgeusia, alopecia, weight loss) and checkpoint-inhibitor irAE — severe cutaneous irAE routed to derm.drug-eruption.core.v1, severe systemic irAE emergent oncology hold. Field-therapy response and adherence reassessed; biopsy any non-resolving or recurrent lesion.
    inputs: inflammatory_markers, creatinine
    actions: panel.cbc, panel.lft, panel.inflammation
    advance: risk-based recurrence/new-primary surveillance schedule set; transplant intensified; systemic-therapy AE/irAE co-monitoring defined
12. 12FOLLOWUP
    Lifelong derm continuity: scheduled total-body skin exams (prior NMSC ≈ strongest predictor of the next; substantial cumulative new-primary risk), structured skin self-examination, rigorous photoprotection counselling, chemoprevention adherence (nicotinamide, acitretin for high-risk/transplant), field-cancerisation re-treatment as needed, transplant-team immunosuppression-modulation continuity, and Gorlin/xeroderma-pigmentosum familial/genetic counselling. Re-stage and re-route to oncology on recurrence/locally-advanced progression; reconcile any checkpoint-inhibitor cutaneous irAE with derm.drug-eruption.core.v1.
    inputs: photodamage_and_risk_factors, prior_nmsc_count_and_sites
    actions: workup.chronic_pruritus
    advance: lifelong surveillance + self-exam + photoprotection + chemoprevention + transplant + familial counselling documented; recurrence/advanced re-entry path defined