Lentigo Maligna: IDS 2026 Guidelines & Mohs Surgery

Lentigo maligna (LM) is melanoma in situ (MIS) occurring on chronically sun-damaged (CSD) skin. It accounts for 5-15% of all melanomas and predominantly affects older adults, with a median age at diagnosis in the 7th to 8th decade. The head and neck region is the most common site, representing over 80% of cases, followed by other sun-exposed areas such as the dorsal forearms. LM incidence has been increasing steadily across all populations studied, a trend attributed to aging demographics, cumulative UV exposure, and improved diagnostic awareness. Molecularly, LM belongs to the CSD melanoma pathway, characterized by a high tumor mutational burden (TMB) driven by UV signature mutations. The most frequent driver mutations are NRAS (found in approximately 15-25% of cases), followed by BRAF (typically non-V600E variants in CSD melanoma), and NF1 loss-of-function mutations. KIT mutations and amplifications also occur, particularly in acral and mucosal variants, but are less common in LM. The high TMB of CSD melanomas has implications for immunotherapy responsiveness if progression to invasive disease occurs. The risk of progression from LM to invasive LMM has been estimated at 2-50% over a patient lifetime, depending on lesion size, duration, and patient age. A commonly cited annual progression rate is approximately 3.5%, though this figure carries substantial uncertainty. Once invasive, LMM follows the same staging and prognosis framework as other melanoma subtypes when controlled for Breslow depth. Because LM is by definition in situ, it carries no metastatic potential unless invasion develops, making complete excision or destruction of the in situ component a curative intervention.

Dermoscopy is the first-line diagnostic tool for evaluating pigmented lesions on sun-damaged skin and is recommended with Grade A evidence by the IDS consensus. The dermoscopic features of LM reflect the proliferation of atypical melanocytes along the dermoepidermal junction and their interaction with adnexal structures. Key dermoscopic criteria include asymmetric pigmented follicular openings (the single most sensitive early sign), slate-gray dots and globules, rhomboidal structures (formed by pigment outlining rete ridges), annular-granular pattern (gray dots surrounding follicular openings), obliteration of follicular openings by pigment, and dark homogeneous blotches in more advanced lesions. The IDS guidelines also endorse the "inverse approach" for facial pigmented lesions (Grade A), which is particularly useful on the face where standard melanoma dermoscopy algorithms (pattern analysis, ABCD rule) perform poorly. The inverse approach works by first evaluating whether a facial lesion shows features of common benign entities - solar lentigo (moth-eaten borders, fingerprint-like structures, sharp demarcation), seborrheic keratosis (milia-like cysts, comedo-like openings, brain-like pattern), lichen planus-like keratosis (granularity without follicular involvement), or pigmented actinic keratosis (strawberry pattern, follicular openings with white halos). If none of these benign patterns are identified and the lesion shows gray color or any LM-specific criteria, LM should be suspected.

Histopathologic confirmation is mandatory (IDS Grade A) before initiating treatment for suspected LM. The histologic hallmark of LM is a proliferation of atypical melanocytes along the dermoepidermal junction of sun-damaged skin, typically in a lentiginous (single-cell) pattern. These melanocytes show nuclear atypia, with enlarged, hyperchromatic, irregular nuclei. In more developed lesions, melanocytes form confluent arrays, extend along adnexal structures (follicular and eccrine duct epithelium), and may exhibit pagetoid scatter into the upper epidermis. A background of severe solar elastosis is characteristic. The key diagnostic challenge is distinguishing true LM from the melanocytic hyperplasia that commonly occurs on chronically sun-damaged skin in older patients. UV-induced melanocytic hyperplasia can produce increased melanocyte density at the junction, but the melanocytes lack the nuclear atypia, confluence, and pagetoid spread seen in LM. This distinction requires experienced dermatopathologic evaluation and is one of the main reasons clinician-pathologist collaboration is emphasized in the IDS guidelines.

Complete surgical excision to negative histologic margins is the first-line treatment for LM (IDS Grade A). However, the IDS consensus notes that no definitive "safe" peripheral margin has been established for standard excision of LM. NCCN recommends 0.5-1.0 cm margins for melanoma in situ, but multiple studies demonstrate that these margins are insufficient for a substantial proportion of LM cases. Studies using serial sectioning show that standard 5 mm margins achieve clearance in only approximately 50% of facial LM, and even 1 cm margins may be inadequate in 10-20% of cases. This is because LM extends subclinically along sun-damaged skin in an irregular, often asymmetric pattern that is poorly predicted by clinical borders. For these reasons, margin-controlled surgical techniques - including Mohs micrographic surgery and staged excision - are the preferred surgical approach for LM, particularly for lesions that are large, ill-defined, recurrent, or located on cosmetically or functionally sensitive sites.

Non-surgical treatments for LM are indicated when surgery is contraindicated (patient comorbidities, surgical refusal), when the lesion extent precludes reasonable surgical excision, or as adjuvant therapy after surgery with narrow margins. The IDS consensus evaluated three non-surgical modalities: radiotherapy, topical imiquimod, and destructive techniques (cryotherapy, laser). Cryotherapy and laser ablation are NOT recommended for LM (IDS Grade B against both), as they do not allow histologic margin assessment and are associated with high recurrence rates due to incomplete destruction of melanocytes within adnexal structures.

LM recurrence rates vary widely depending on the treatment modality and margin status, ranging from less than 3% after margin-controlled excision (slow Mohs) to over 40% after standard excision with inadequate margins or non-surgical treatment. Narrow histologic margins (less than 0.2 mm from the nearest atypical melanocyte) are a significant predictor of recurrence after standard excision. Recurrence can be delayed - the mean time to recurrence exceeds 57 months in several series, and recurrences have been reported more than 10 years after initial treatment. This mandates long-term follow-up. The IDS consensus recommends combined clinical, dermoscopic, and RCM monitoring (clinical plus dermoscopy: Grade A). Dermoscopy is particularly valuable because recurrent LM often manifests as subtle gray dots or asymmetric pigmented follicular openings at the scar margin before it becomes clinically visible. RCM can detect recurrence at the cellular level and is recommended for equivocal findings on dermoscopy.

The 2026 IDS Consensus Guidelines by Forsea et al. provide graded recommendations for all aspects of LM management, based on evidence quality and expert agreement among 53 dermoscopy and dermatologic surgery experts from 20 countries. The following table summarizes the key recommendations and their grades.