There are numerous skin cancers for which radiotherapy provides an organ-preserving method of elimination. Australia has the highest rate of skin cancers in the world and skin cancer is the most commonly seen malignancy in the country.
The anatomy of the skin is important for both the development of malignancy as well as the consideration of treatment options.
Specific Cancer Types
Basal cell carcinoma is the most common malignancy in humans and occurs most frequently in Caucasian populations. Surgical treatment is usually indicated. Radiotherapy may be indicated when:
- Patients decline or are unfit for surgery
- Tumours are located in cosmetically complex areas (eg. nose, lip, ear, periorbital)
- Adjuvantly for tumours have positive margins, perineural invasion, or are of morphaeic type with close margins.
Dose is 60 Gy in 30 fractions although hypofractionation (50/20, 40/15) may be appropriate for small lesions away from critical structures (eg. eye). Margins are 0.5 cm GTV->CTV for small nodular lesions but 1 cm all other types; morphaeic BCC with indistinct margins should have 1.5 cm added at least. Elective nodal irradiation is never used. Those with perineural invasion of named nerves should have that nerve traced back to the base of skull (eg. superior orbital fissure, foramen rotundum, foramen ovale (V3) or the stylomastoid foramen (VII).
Squamous cell carcinoma is the second most common malignancy in humans and has a similar aetiology to basal cell carcinoma. Precursor lesions include actinic keratosis (aka solar keratosis) which is treated with topical therapy or Bowen's disease which is treated with topical therapy, excision or radiotherapy. High risk features necessitation larger radiotherapy margins or elective nodal irradiation include depth > 2 mm, size > 2 cm, high risk location (ear/nose/lip), perineural invasion. Radiotherapy is indicated for:
- Primary Treatment
- Patients who decline or are unfit for surgery
- Cosmetically difficult areas as per BCC
- Dose is typically 60 Gy in 30 fractions (consider raising to 66 Gy for neglected bulky tumours)
- Margins are 1 cm for small well differentiated lesions but 2 cm for high risk tumours.
- Adjuvant Treatment
- Always indicated when margins are positive and surgery is not possible or would result in poor cosmesis
- May be indicated for patients with multiple high risk features
- Often used for patients with nodal metastases (treatment of involved level + draining level eg: parotid nodes + level II) - 60 Gy to macroscopic disease, 50 Gy elective neck
Merkel cell carcinoma is the neuroendocrine tumour of the skin. It is a rare tumour but is highly aggressive both locally and distantly. Recommendations for wide local excision with adjuvant radiotherapy (50 Gy) to the tumour bed are typical, although primary radiotherapy (60 Gy) can be used with wide margins of 5 cm. The regional nodes should be staged with sentinel node biopsy; if microscopically positive then nodal regions should be treated with surgery or radiotherapy (50 Gy); adjuvant nodal irradiation is used in cases of extracapsular extension (50 Gy). Macroscopic nodes should be treated with lymph node dissection.
Systemic therapy has a role in metastatic disease and is also the subject of clinical trials.
A variety of lymphoma types can occur in the skin, including Mycosis Fungoides, indolent B cell lymphomas (follicle centre lymphoma/MALT lymphoma), and aggressive lymphomas (DLBCL leg-type and non-leg type).
- Mycosis fungoides is treated with PUVA therapy in early stages. Thick plaques and tumours require deeper treatment, usually with electron therapy. Extensive disease can be treated with total skin electron therapy using a variety of techniques. Sezary syndrome is the leukaemic phase of mycosis fungoides and is treated with systemic therapy and palliative radiotherapy to bulky sites.
- Indolent B cell lymphomas are the most common cutaneous B cell lymphoma and are treated curatively with local radiotherapy to the tumour site. The total dose is 30 Gy in 15 fractions. This provides a 99% complete response rate and long term cure in 90%. Tumours that involve adjacent lymph node sites should have these covered also.
- Aggressive B cell lymphomas are treated with local radiotherapy with systemic R-CHOP. Involved field radiotherapy should cover the tumour site and the first echelon nodes. Dose is 36 Gy in 15 fractions.