Diagnostic considerations

Pigmented lesion changes in pregnancy — physiological hyperpigmentation (linea nigra, melasma, generalised), benign naevus enlargement and darkening (oestrogen / progesterone-driven). However, any lesion meeting ABCDE criteria (asymmetry, border, colour, diameter, evolution) should still be biopsied — pregnancy does not exempt suspicious lesions from biopsy.
Excisional biopsy is safe in any trimester under local anaesthetic; lignocaine ± adrenaline is acceptable.
Photographic / dermoscopic documentation of any borderline lesion at the start of and during pregnancy is recommended.
Histology — encourage early reporting; specialist dermatopathology if equivocal Spitz / atypical / borderline lesions in pregnancy.

Staging investigations

Ultrasound (regional nodes, liver) — preferred initial imaging in pregnancy; no foetal radiation.
MRI without gadolinium — preferred for brain and other deep imaging in pregnancy; gadolinium contraindicated due to foetal accumulation.
Chest X-ray with abdominal shielding — acceptable; foetal dose negligible.
CT chest / abdomen / pelvis with abdominal shielding — acceptable when essential; foetal dose <5 mGy in second / third trimester (below the 50 mGy threshold for foetal harm).
PET-CT — relatively contraindicated in pregnancy due to foetal F-18-FDG uptake; alternative imaging preferred unless essential.
Sentinel lymph node biopsy with technetium-99m — feasible; foetal radiation dose <1 mGy; avoid blue dye (allergic reaction risk + foetal safety unknown). Most clinicians defer SLNB to after delivery if oncologically reasonable, but it can be performed in pregnancy if needed.

Wide local excision — safe in any trimester under local anaesthetic.
General anaesthesia for larger / multifocal / SLNB cases — safe in second and third trimesters; first trimester anaesthesia carries small theoretical risk of teratogenicity (period of organogenesis); consult obstetric anaesthetic / maternal-foetal medicine.
Mohs micrographic surgery — safe; preferred for facial / cosmetically critical sites.
Reconstruction — primary closure, local flaps and skin grafts safe; large free-flap reconstruction may be delayed to post-delivery if non-urgent.
Caesarean delivery for skin cancer — rarely indicated; consider only for advanced disease where delivery enables systemic therapy or for placental metastasis (rare; melanoma is the commonest cancer to metastasise to placenta).

BRAF / MEK inhibitors (dabrafenib, trametinib, encorafenib, binimetinib) — teratogenic / embryo-foetal risk; contraindicated in pregnancy unless life-threatening disease where benefits outweigh risks.
Immune checkpoint inhibitors (pembrolizumab, nivolumab, ipilimumab, cemiplimab, avelumab) — placental transfer of IgG monoclonal antibodies; theoretical risk of immune-related adverse events in foetus / neonate. Limited data; generally avoid in pregnancy unless life-threatening disease.
Hedgehog pathway inhibitors — potent teratogens producing severe craniofacial / skeletal abnormalities and strictly contraindicated in pregnancy. Post-treatment contraception windows differ: vismodegib requires avoidance of pregnancy for 24 months after the last dose in the UK SmPC; sonidegib labelling specifies at least 20 months for female patients of reproductive potential and 8 months condom use for male patients with female partners. Confirm current product information before prescribing.
Conventional chemotherapy — acceptable in second / third trimester for haematological malignancy; first-trimester chemotherapy is teratogenic.
Radiotherapy — contraindicated in pregnancy (foetal radiation dose).
Topical therapies — 5-FU, imiquimod, hydroquinone are potentially harmful in pregnancy; avoid; topical retinoids contraindicated; oral retinoids strictly contraindicated.

Historical concern that pregnancy independently worsens melanoma prognosis has been largely refuted by modern observational studies — stage-matched survival is comparable to non-pregnant matched controls.
Some adverse features at presentation (more advanced stage, thicker tumours) may reflect delayed diagnosis ("any new mole in pregnancy is just hormonal") and surveillance lapses rather than biological aggression.
Future pregnancies after melanoma — current evidence does not suggest pregnancy increases recurrence; women treated for melanoma should not be advised to avoid future pregnancies on melanoma grounds.
Placental and neonatal metastasis — exceedingly rare but well-described for melanoma; placenta should be sent for histology in all pregnancies of women with metastatic melanoma.

Skin cancer MDT + obstetric / maternal-foetal medicine + oncology + neonatal medicine + (often) clinical genetics.
Counsel about diagnostic / therapeutic limitations and risks.
Consider timing of delivery — early delivery for advanced disease enabling systemic therapy; routine delivery and standard care for early-stage / localised disease.
Photographic surveillance of all naevi; biopsy any change without delay.
Counsel about safe sun protection in pregnancy (mineral / inorganic sunscreens preferred over chemical).