Welcome back to the journal review. This month we're in the December twenty twenty-five issue of the Journal of the American Academy of Dermatology, and we've got a two-part continuing medical education series on lentigo maligna that's well worth your time — Part One covers epidemiology, risk factors, and diagnosis, and Part Two covers management. Given that this is a paired CME review rather than a single original study, I'll walk through each as the authors present it — a synthesis of the current evidence base rather than a single trial with its own methods and results.

Let's start with Part One. This is a review article, and it opens by tackling something that trips up even experienced readers of pathology reports: nomenclature. The authors are explicit that lentigo maligna and lentigo maligna-type melanoma in situ are used interchangeably in this review, describing the atypical intraepidermal precursor to invasive lentigo maligna melanoma. They also carve out a separate entity — lentiginous melanocytic hyperplasia — which is just increased basilar melanocytes without nesting, confluence, or pagetoid spread, essentially a field effect on sun-damaged skin that you don't want to conflate with true lentigo maligna. That distinction matters every time you're reading a biopsy report on a background of chronic photodamage.

On epidemiology, the numbers are worth having ready for patient conversations. Lentigo maligna is the dominant subtype of melanoma in situ, making up roughly four out of five cases in the Surveillance, Epidemiology, and End Results data, while the invasive counterpart, lentigo maligna melanoma, accounts for a much smaller slice — somewhere between one in twenty and one in seven of all invasive melanomas. About two-thirds of patients are men, it's overwhelmingly a disease of White patients, and just over half of diagnoses occur after age seventy. Incidence has been climbing steadily — age-standardized rates went from about four to about five and a half per hundred thousand person-years over the two thousands into the twenty-tens — and the authors note this rise is probably a mix of genuine increased ultraviolet exposure over a lifetime and increased diagnostic scrutiny, meaning more skin exams, lower biopsy thresholds, and sharper pathologic interpretation.

The progression risk discussion is honestly the most clinically important — and most humbling — part of this section. Reported lifetime transformation rates to invasive melanoma range enormously in the literature, from about two percent up toward fifty percent, which tells you the field simply doesn't have great prospective data here. Weinstock's SEER analysis pegged annual malignant transformation risk at a fraction of a percent per year, with lifetime risk in the low single digits, while a more recent analysis by Menzies estimated an annual progression rate of about three and a half percent, with an average time to progression pushing toward three decades. The authors' takeaway, and I think it's the right one clinically, is that there's probably no constant annual hazard — the latency for any given lesion is unpredictable, and only a subset of lentigo maligna lesions likely carry real biologic potential to invade. Worth remembering too: recurrence of invasive melanoma after treatment of melanoma in situ has been noted around five years out on average in salvage Mohs cohorts, which reinforces that your surveillance window needs to extend well past the typical short-term follow-up horizon.

Risk factors are what you'd expect — cumulative ultraviolet exposure from both the ultraviolet B and the deeper-penetrating ultraviolet A range, fair skin, and a personal history of other chronic-sun-damage lesions like actinic keratosis and squamous cell carcinoma.

Clinically, the review emphasizes that lentigo maligna is a diagnostic moving target — a flat, tan-brown macule or patch on chronically sun-damaged skin, most classically the cheek, though there's a notable sex difference, with men showing more scalp and ear involvement. Borders start regular and become irregular and notched as the lesion enlarges, pigmentation becomes heterogeneous, and pink or white areas can signal regression or a desmoplastic component underneath — which is a real concern, since desmoplastic melanoma is often found beneath a lentigo maligna and may not be reliably detected by palpation. The subclinical spread issue is the crux of everything that follows in Part Two: one study found subclinical pathologic lentigo maligna in about one in five cases even after six-millimeter surgical margins, which tells you why standard oncologic margins for melanoma in situ elsewhere on the body don't translate cleanly to the face and scalp.

On diagnostic adjuncts, the review walks through Wood's lamp — useful for accentuating epidermal melanin and helping define lateral margins, but it can't see dermal melanocytes and it tends to overestimate margins because of surrounding mottled photodamage, so it's not a tool for distinguishing benign from malignant. Dermoscopy gets more real estate, with a list of features you likely already use — gray color, perifollicular granularity, asymmetric follicular openings, circle-within-circle structures, and angulated lines coalescing into rhomboids. And reflectance confocal microscopy is flagged as diagnostically superior to dermoscopy, though its use remains limited by availability and the learning curve required for expertise — an important caveat if you're at a center without RCM access.

Now to Part Two, the management review, which is really the actionable half for those of us doing the cutting.

The framing up front is important: surgery remains first-line, but there is no single agreed-upon optimal technique, and outcomes hinge on close coordination between surgeon and pathologist. The review lays out a guideline comparison across the National Comprehensive Cancer Network, the American Academy of Dermatology, the European Association of Dermato-Oncology, and Cancer Council Australia — and while the exact wording differs, they converge on the same idea, that lentigo maligna often needs more than the standard five-millimeter margin used for melanoma in situ elsewhere, sometimes a centimeter or more, because of that same subclinical spread problem from Part One.

Conventional excision with five millimeter to one centimeter margins is described as historically the default, but the review is blunt that recurrence rates after conventional excision have been reported as high as twenty percent in some series — a number that clearly drove the shift toward margin-controlled techniques.

Mohs micrographic surgery gets substantial coverage, and the numbers here are the ones worth quoting to a patient or a tumor board. Upstaging to invasive disease on the debulk specimen occurs in about five to eight percent of cases — a good reminder to always process that central debulk with vertical sections before you start worrying about peripheral margins. Recurrence rates with the en-face Mohs technique cluster mostly in the zero to one percent range, with the overall reported range up to about six percent and one outlier study at thirty-three percent, though that was a very small cohort of eighteen patients, so I wouldn't weight it heavily. A systematic review pooling over a hundred manuscripts and roughly fourteen thousand head and neck melanomas found local recurrence of about zero point six percent after Mohs compared to almost eight percent after wide local excision — a striking gap, but the authors are careful to flag that the wide excision cohort had a higher proportion of invasive melanomas, which likely inflated that comparison, and that most included studies didn't use a consistent definition of local recurrence. So take the direction of that finding seriously, but hold the magnitude a little loosely. One technical pearl: frozen section processing can distort perinuclear retraction artifacts that you rely on to identify melanocytes, and the review notes that adding MART-1 or MITF immunostaining to frozen sections is comparable or better than permanent sections for margin clearance, and is associated with even lower recurrence, down around zero to half a percent — so if you're not already reflexively staining frozen sections for lentigo maligna cases, this is a straightforward, practice-reinforcing point.

Staged excision techniques — the square procedure, the spaghetti technique, geometric staged excision — are presented as a reasonable alternative built around permanent section processing, which is still the pathologic gold standard, at the cost of a delayed reconstruction while margins are read over a day or two. Reported local recurrence with these techniques ranges from zero up to about nine percent, comparable in ballpark to Mohs, though obviously without same-day closure.

Reflectance confocal microscopy comes back here specifically as a presurgical mapping tool. The review cites margin positivity as high as forty-five percent using traditional clinical and dermoscopic margin assessment, dropping to as low as five percent when RCM is incorporated, and a meta-analysis of five studies with a bit under two hundred patients found RCM reduced positive margins, reduced the number of surgical stages, lowered local recurrence, and meaningfully cut time to repair. Concordance between RCM and histopathology was strong in two prospective cohorts, in the high eighty percent range — good enough to trust as an adjunct, though again gated by equipment and expertise.

For nonsurgical management, the review is appropriately narrow — this is for patients who are poor surgical candidates or who decline surgery. Topical imiquimod is discussed as a primary option in that setting, working through toll-like receptor 7 and 8 activation to drive a local inflammatory response, and radiotherapy is the other modality specifically endorsed in the current AAD guidelines. Active surveillance is raised as a reasonable path for older patients with significant comorbidities, paired with structured self-examination education.

So, pulling this together for practice. The genuinely practice-reinforcing points here are ones many of you are likely already doing: margin-controlled excision — Mohs or staged excision — over conventional wide excision given the well-documented subclinical spread and the real recurrence gap; reflexive use of MART-1 or MITF immunostaining on frozen sections to sharpen margin calls; and surveillance intervals that extend well beyond a couple of years, given that recurrences have shown up around five years out and progression latency can run decades. The more forward-looking, "interesting but not yet standard" piece is reflectance confocal microscopy for presurgical mapping — the data are promising for reducing positive margins and stage number, but availability and operator expertise remain real-world bottlenecks, so I'd call that an emerging adjunct rather than a mandate. And diagnostically, keep Wood's lamp in its proper lane — margin orientation and monitoring, not a rule-in or rule-out tool — while leaning on dermoscopy's specific pattern list for your day-to-day discrimination from solar lentigines and pigmented actinic keratoses.

That wraps our two-part deep dive into lentigo maligna this month. Thanks for listening, and we'll see you next episode.