Lentigo maligna: radiotherapy and soft X-rays

Its place in treatment

Lentigo maligna is melanoma in situ, usually on chronically sun-exposed skin. Surgery remains the reference treatment because it allows removal and examination of tissue. When an operation is impractical or would cause unacceptable functional or cosmetic consequences, the team may discuss alternatives in selected cases.

Radiotherapy uses ionising radiation to treat the affected area. Soft X-rays and Grenz rays are superficial techniques, but they are not synonymous with every form of radiotherapy. Energy, penetration and delivery differ between devices: a published dose for one technique cannot be transferred to another.

An invasive component changes the assessment. This page does not propose superficial radiotherapy as a general treatment for invasive or metastatic melanoma. Before choosing an alternative to excision, an adequate histological diagnosis and specialist assessment of extent are necessary.

Sources for this section: American Academy of Dermatology — Melanoma clinical guideline; Hedblad and Mallbris — Grenz ray treatment, 593 patients, JAAD (2012).

The Stockholm study: what it documented

Hedblad and Mallbris published a 2012 series of 593 patients treated at Karolinska between 1990 and 2009: 350 received Grenz rays as primary treatment, 71 after partial excision and 172 after complete excision. These different groups do not constitute a randomised comparison with surgery.

The authors reported complete clearance after one fractionated course in 520/593 patients, or 88%; 15 had residual lesions and 58 experienced recurrence. Follow-up was at least two years for 425 patients and five years for 241. This does not mean definitive cure in 88% at an identical follow-up point for everyone.

The paper described six sessions over three weeks and total doses of 100–160 Gy specific to Grenz rays. These are historical protocol data, not instructions for treating a patient today or using another device. The previous page also reported “53 recurrences, 72%”: that percentage is inconsistent with a denominator of 58 and is not reproduced as a reliable figure.

Sources for this section: Hedblad and Mallbris — Grenz ray treatment, 593 patients, JAAD (2012).

Later evidence and comparison with imiquimod

A later study with ten-year follow-up, published in 2020, reported favourable outcomes in a Grenz-ray-treated cohort. It remains observational experience from a specialist setting: it does not establish suitability for every lentigo maligna or equivalence to surgery in all patients.

A phase III randomised study comparing radiotherapy and imiquimod in 126 patients with lentigo maligna unsuitable for surgery was published in 2025. At six months, response was 95% in both groups; at 24 months, 12 treatment failures were reported with radiotherapy and 6 with imiquimod. The difference was not statistically significant, and early termination of recruitment reduced the study’s statistical power.

These findings do not prove equivalence between the options, and neither was directly compared with surgery in this trial. Initial response and durable control are also different outcomes. Decisions must additionally consider tolerability, site, adherence, follow-up feasibility and the individual’s preferences.

Sources for this section: Ten-year follow-up of Grenz ray treatment (2020); Hong et al. — Radiotherapy versus imiquimod, randomized phase 3 trial, JAAD (2025).

Before and after treatment

Planning is the responsibility of the radiation oncologist and the team managing the lesion. It is important to clarify which area will be treated, how its boundaries were assessed and how possible invasion was investigated or excluded. A partial sample does not always represent the entire lesion: nodular areas or areas differing from the rest may need further assessment.

The pathway involves repeated appointments and skin reviews. Local inflammatory reactions and skin changes should be discussed before starting; “nonsurgical” does not mean free of adverse effects or practical demands. A favourable cosmetic result in a published series is not an individual guarantee.

After treatment, disappearance of pigmentation alone does not certify absence of disease. The team determines follow-up and whether biopsies are needed. New pigmentation, nodules or changes in the treated area require reassessment. Recurrence may require a different approach after diagnosis and extent have been clarified.

Sources for this section: Hong et al. — Radiotherapy versus imiquimod, randomized phase 3 trial, JAAD (2025); American Academy of Dermatology — Melanoma clinical guideline.

Selected use, research and limitations

Radiotherapy should not generically be described as an experimental novelty: it has a clinical history and a selected role in lentigo maligna. Questions remain about comparisons between techniques, patient selection and long-term outcomes. Use within a study and specialist clinical use are not the same thing.

If an experimental protocol is proposed, ask which question it addresses, which established alternatives exist and how response and safety will be assessed. Consent should include risks and uncertainties. The surgical treatment guide contains a dedicated experimental-treatment section; this page does not replace dermatological, surgical and radiation-oncology consultation.

Sources for this section: American Academy of Dermatology — Melanoma clinical guideline; National Cancer Institute — Participate in Cancer Treatment Trials.