12-phase flow (12)

1. 1FRAME
   Frame BCC as the most common cancer in fair-skinned populations — locally destructive, rarely metastatic. The dermatology engine owns recognition, biopsy, NCCN risk stratification, definitive local therapy (Mohs / excision / ED&C / topical / RT) AND the locally advanced/metastatic systemic ladder (HHI → cemiplimab), routing only the rare bona-fide visceral metastatic / skull-base disease to multidisciplinary care. Gorlin syndrome and field cancerisation overlap with SCC and melanoma are recognised here.
   advance: derm-owned scope set; sibling routes (SCC, AK-NMSC, melanoma) noted
2. 2ENTRY
   Recognise a pearly papule with arborising vessels, a non-healing/bleeding lesion, a scar-like morphoeic plaque, a pigmented arborising-vessel lesion (melanoma-mimic), or a Gorlin/transplant-surveillance entry. Capture subtype morphology up front.
   inputs: lesion_morphology_and_subtype
   actions: workup.chronic_pruritus
   advance: entry trigger recognised; subtype morphology recorded
3. 3CONTEXT
   Build the recognition context: dermoscopy (arborising telangiectasia, blue-grey ovoid nests, leaf-like / spoke-wheel areas, ulceration), full-body skin exam for synchronous BCC + AK + SCC + melanoma, Gorlin-syndrome features (palmar/plantar pits, odontogenic keratocyst history, hypertelorism, falx calcification, medulloblastoma family history), UV burden, organ-transplant / immunosuppression status, and field-cancerisation context.
   inputs: dermoscopy_findings, gorlin_basal_cell_nevus_syndrome_features
   actions: workup.chronic_pruritus
   advance: dermoscopy + total-body skin exam done; syndromic / immunosuppression context established
4. 4RED_FLAGS
   Perineural invasion symptoms (pain, paraesthesia, motor weakness along a named nerve such as V or VII branches) → cross-sectional imaging + multidisciplinary care. Locally advanced disease invading bone / orbit / cartilage / muscle — surgically unresectable or unacceptable morbidity. Bona-fide metastatic disease (regional nodes, lung, bone) — extremely rare (<0.1%) but mandates systemic + multidisciplinary management. Suspected basosquamous histology (hybrid BCC/SCC) shifts management toward SCC-grade aggression.
   inputs: perineural_or_motor_sensory_symptoms
   actions: panel.cbc, panel.inflammation
   advance: PNI/locally-advanced/metastatic flags screened and imaging/MDT routed if positive
5. 5INITIAL_WORKUP
   DIAGNOSTIC BIOPSY: shave or punch biopsy of the most representative area is acceptable for BCC (unlike melanoma; shave does not compromise BCC management because BCC is not Breslow-staged). Histology should report subtype (nodular / superficial / micronodular / infiltrative / morphoeic / basosquamous), depth, perineural invasion, lymphovascular invasion, and margin status when an excision specimen. Routine bloods / imaging are NOT indicated for asymptomatic localised low/intermediate-risk BCC; obtain baseline labs only when systemic therapy is anticipated.
   inputs: lesion_morphology_and_subtype, cbc_with_differential, lft
   actions: panel.cbc, panel.lft
   advance: biopsy obtained with subtype reported; baseline labs drawn if HHI/cemiplimab anticipated
6. 6BRANCHING_WORKUP
   Histopathology-driven branch: nodular / superficial low-risk → ED&C, excision 4 mm, or topical (superficial only). Aggressive subtype (morphoeic, micronodular, infiltrative, basosquamous), PNI, deep invasion, recurrent, or H-zone / immunosuppressed → Mohs micrographic surgery OR excision with intra-operative frozen-section circumferential margin assessment. Locally advanced (unresectable / unacceptable morbidity) or metastatic → cross-sectional imaging (CT/MRI for PNI/orbit/bone; CT chest-abdomen for distant) + systemic HHI ± cemiplimab.
   inputs: staging_imaging_for_locally_advanced_or_metastatic
   actions: panel.inflammation
   advance: risk tier (low / high / locally advanced / metastatic) assigned; appropriate imaging done; treatment route selected
7. 7DIFFERENTIAL
   Terminal differential with named pivots: BCC vs squamous-cell carcinoma (hyperkeratotic firm plaque + tender + faster growing — route derm.squamous-cell-carcinoma-skin.core.v1) vs actinic keratosis (rough hyperkeratotic macule on UV-damaged field — route derm.actinic-keratosis-nmsc.core.v1) vs sebaceous hyperplasia (yellowish umbilicated papule, crown-vessels dermoscopy pivot) vs intradermal nevus (soft skin-coloured papule, no telangiectasia pivot) vs molluscum contagiosum (central umbilication, often multiple pivot) vs pigmented seborrheic keratosis (stuck-on, milia-like cysts pivot) vs MELANOMA (asymmetric network, blue-white veil — route derm.melanoma.core.v1 if any doubt — pigmented BCC is the principal melanoma-mimic) vs fibrous papule (firm conical papule, nose) vs Merkel-cell carcinoma (rapidly growing, red-purple, immunosuppressed-elderly — high suspicion → urgent biopsy + MDT). Field cancerisation means BCC + SCC + AK frequently co-exist.
   advance: best diagnosis selected; pigmented-BCC-vs-melanoma branch resolved by biopsy if any doubt
8. 8RISK_STRATIFICATION
   NCCN BCC 2025 risk grouping (schema-blocked as a TS calculator — captured narratively): LOW-risk = trunk/extremity <2 cm (L zone), no aggressive features, primary, immunocompetent, no PNI, well-defined borders, non-aggressive histologic subtype. HIGH-risk = any H-zone, M-zone ≥1 cm, L-zone ≥2 cm, ill-defined borders, recurrent, immunosuppressed, site of prior RT, aggressive histologic subtype (morphoeic / micronodular / infiltrative / basosquamous / sclerosing), PNI. Risk tier drives the local therapy choice; locally advanced / unresectable / metastatic disease is a separate tier requiring systemic therapy.
   inputs: anatomic_site_h_m_l_zone, tumor_size_and_borders, recurrence_immunosuppression_prior_rt
   advance: NCCN risk tier (low / high / locally advanced / metastatic) assigned
9. 9TREATMENT
   RISK-DIRECTED LOCAL THERAPY (NCCN BCC 2025). LOW-RISK: standard surgical excision with 4-mm clinical margins (non-pharm) OR electrodesiccation-and-curettage (non-pharm, NOT on terminal-hair-bearing sites) OR cryosurgery (non-pharm) OR for superficial BCC only — topical imiquimod 5% 5x/wk x 6 wk OR topical 5-fluorouracil 5% BID x 3-6 wk OR photodynamic therapy. HIGH-RISK: MOHS micrographic surgery (preferred) OR excision with intra-operative frozen-section complete-margin assessment OR definitive radiotherapy (non-surgical candidate). LOCALLY ADVANCED / METASTATIC / RECURRENT-AFTER-MOHS: Hedgehog-pathway inhibitor — vismodegib 150 mg PO daily (ERIVANCE PMID 22670903) or sonidegib 200 mg PO daily (BOLT PMID 25981810 / Dummer 33358380). HHI-refractory or HHI-intolerant: cemiplimab 350 mg IV q3wk (Stratigos PMID 34000246). Gate on pregnancy (HHI EMBRYOFETAL TOXIC — boxed warning), Gorlin (AVOID ionising radiation), and HHI-class toxicities (muscle spasm, alopecia, dysgeusia, weight loss).
   inputs: pregnancy_status, creatinine_and_egfr
   advance: risk-appropriate local therapy chosen OR systemic ladder started for advanced disease; pregnancy + Gorlin gates applied
10. 10DISPOSITION
    Almost entirely outpatient: ED&C / excision / Mohs / topical / cryotherapy / HHI start are all outpatient procedures. Multidisciplinary tumour-board referral for locally advanced / PNI / orbital-bony invasion / planned reconstructive flap / metastatic disease. Radiation oncology referral for definitive RT or adjuvant RT for PNI / positive deep margin. Genetics referral for suspected Gorlin (≥2 BCCs <30 y, ≥5 BCC lifetime, or syndromic features).
    inputs: perineural_or_motor_sensory_symptoms
    advance: disposition documented; MDT / radiation oncology / genetics referrals made as indicated
11. 11MONITORING
    Surveillance: total-body skin exam every 6-12 months for life (60-90% lifetime risk of a second BCC after a first; rises further in Gorlin, organ transplant, prior RT). On HHI: monitor for muscle spasm / cramps (manage with hydration, magnesium, dose holds; serum CK if severe), alopecia, dysgeusia, weight loss, hepatic transaminases (LFT), and pregnancy status in any female of reproductive potential (contraception during + 24 months after vismodegib, 20 months after sonidegib per labelling). On cemiplimab: immune-related adverse events (skin, thyroid, hepatitis, colitis, pneumonitis, hypophysitis, myocarditis).
    inputs: cbc_with_differential, lft
    actions: panel.cbc, panel.lft
    advance: lifelong skin surveillance + agent-specific monitoring schedule set
12. 12FOLLOWUP
    Lifelong derm continuity: photoprotection (broad-spectrum SPF ≥30, sun-protective clothing, behavioural avoidance), skin self-examination education, family / Gorlin counselling, chemoprevention discussion (nicotinamide 500 mg BID — ONTRAC trial NEJM PMID 26488693 reduced new NMSC ~23% in high-risk patients; consider for those with multiple BCC / SCC / dense field). Organ-transplant recipients receive intensified surveillance and individualised immunosuppression review with transplant team. Recurrence at the prior site → re-biopsy + escalate to Mohs / margin-assessed excision; new advanced / metastatic disease → re-enter systemic ladder.
    inputs: gorlin_basal_cell_nevus_syndrome_features, recurrence_immunosuppression_prior_rt
    actions: workup.chronic_pruritus
    advance: photoprotection + self-exam + chemoprevention + surveillance schedule documented