The Bottom Line

Mohs surgery is not the standard treatment for most melanomas. However, for a specific type called lentigo maligna (LM) and lentigo maligna melanoma (LMM)—which tend to appear as large, irregular patches on the sun-damaged skin of the face—modified Mohs techniques can offer excellent cure rates while preserving more facial tissue than wide local excision. If your doctor recommends Mohs for melanoma, it is almost certainly because you have LM or LMM in a location where tissue conservation matters greatly.

Understanding Lentigo Maligna and Lentigo Maligna Melanoma

Melanoma has several subtypes, and they do not all behave the same way. Lentigo maligna (LM) is a slow-growing form of melanoma in situ (confined to the top layer of skin) that appears as a large, flat, irregularly shaped patch—often tan, brown, and multi-colored—on chronically sun-damaged skin. The face, particularly the cheeks, nose, and ears, is the most common location. It tends to occur in older adults and grows slowly over years to decades.

When LM begins to invade deeper into the skin, it becomes lentigo maligna melanoma (LMM)—a true invasive melanoma. LMM accounts for about 4–5% of all melanomas but represents a higher proportion of melanomas in elderly patients and on the head and neck.

What makes LM and LMM challenging is that their borders are often much more extensive than they appear to the naked eye. Melanoma cells can spread along sun-damaged skin in a way that is invisible without microscopic examination. Standard clinical margins (the distance you try to cut around the visible tumor) are frequently inadequate for these lesions.

Standard Melanoma Treatment vs. Mohs-Based Approaches

For most invasive melanomas (not LM/LMM type), the standard treatment is wide local excision (WLE): removing the melanoma with 1–2 cm margins of normal-looking skin depending on the tumor’s thickness. This is not typically done with Mohs surgery because traditional melanoma pathology requires specific processing techniques (formalin fixation and permanent sections) that are different from the frozen-section technique used in standard Mohs.

For LM and LMM, Mohs-based approaches have been adapted specifically to address the challenge of incomplete margins. The two most commonly used methods are:

  • Modified Mohs surgery (slow Mohs): Instead of examining frozen sections, tissue is processed with permanent sections—the same method used for regular pathology—which provides better visualization of melanocytes. This means patients wait overnight or longer between stages, but the margin assessment is very accurate.
  • Staged excision with margin control (also called “Square procedure” or “peripheral margin control”): The border of the lesion is removed in segments and examined, with the central tumor removed after clear margins are confirmed on the periphery.

Why Mohs-Based Techniques Are Useful for LM and LMM

The primary advantages for these specific lesions are:

  • Higher cure rates: Studies show recurrence rates of 0–6% for Mohs-based approaches for LM/LMM on the face, compared with recurrence rates of 8–20% with standard excision using conventional margins
  • Tissue conservation: LM lesions can be very large (some span several centimeters across the cheek or nose). Taking 1 cm margins around a 4 cm lesion would result in a 6 cm wound—requiring major reconstruction. Mohs techniques allow removal of only the tissue that is actually involved with cancer.
  • Same-day or near-same-day margin clearance: Knowing the margins are clear before reconstruction allows the reconstructive surgeon to plan appropriately

What to Expect if You Are Having Mohs for LM or LMM

Because “slow Mohs” or staged excision for LM/LMM requires permanent section processing, the procedure usually takes more than one day:

  1. Day 1: The outer border of the lesion is excised in sections, mapped, and sent to the lab for permanent section processing. The wound is dressed temporarily.
  2. Results (24–48 hours later): The pathologist examines the sections and identifies any areas with residual melanoma cells.
  3. Additional stages (if needed): Targeted re-excision of positive areas, with another round of permanent section processing. This may repeat until all margins are clear.
  4. Reconstruction: Once margins are confirmed clear, reconstruction is planned and performed. For large facial defects, this may involve a skin flap, skin graft, or referral to a reconstructive specialist.

This multi-day process can be emotionally challenging. It helps to have a support person who can drive you and accompany you to appointments.

When Is Mohs NOT Appropriate for Melanoma?

Mohs surgery is not the right approach for:

  • Invasive melanomas that are not of the LM/LMM subtype (nodular melanoma, superficial spreading melanoma, acral melanoma, etc.)—these require wide local excision and often sentinel lymph node biopsy
  • Thicker melanomas (Breslow thickness >1 mm or higher) which have an increased risk of lymph node involvement and require additional staging workup
  • Melanomas on the trunk, extremities, or other areas where tissue conservation is less critical

If you have been diagnosed with melanoma other than LM/LMM, your treatment team will recommend wide local excision with specific margin widths based on the tumor’s characteristics.

When to See a Dermatologist

  • You notice an irregularly shaped, multi-colored flat spot on your face, especially on sun-damaged skin, that has grown or changed over time
  • You have been diagnosed with lentigo maligna and want to discuss all surgical options
  • You have had a previous melanoma or LM and notice new suspicious pigmentation near the surgical site
  • You are concerned about a previous incomplete excision of a melanocytic lesion

Frequently Asked Questions

Is Mohs surgery for melanoma experimental?

For LM and LMM specifically, Mohs-based techniques (particularly modified Mohs with permanent sections and staged excision) are well-established and supported by multiple studies showing high cure rates. They are considered appropriate treatment by major dermatologic surgery organizations for LM/LMM in appropriate candidates. They are not experimental for this indication.

Do I still need a sentinel lymph node biopsy with Mohs for LMM?

Sentinel lymph node biopsy (SLNB) is recommended for invasive melanomas thicker than 0.8–1 mm to check whether the cancer has spread to nearby lymph nodes. Whether you need SLNB alongside your Mohs surgery depends on the thickness (Breslow depth) of your LMM. Your dermatologist and surgical oncology team will advise you on this. LM in situ (not yet invasive) does not require SLNB.

Why did my doctor say my LM margins looked clear but the tumor was still big?

LM is notorious for extending far beyond its visible borders. Studies have shown that the actual subclinical extent of LM can be 5 mm to over 1 cm beyond what is visible to the naked eye or even with a dermatoscope. This is precisely why standard “look and cut” excision so often leaves behind microscopic disease, and why margin-controlled techniques have become the preferred approach for this subtype at many Mohs centers.

What are the chances my LM comes back?

With Mohs-based techniques achieving confirmed clear margins, recurrence rates for LM are generally low—reported at 0–6% in most published series, compared with recurrence rates of 8–20% with conventional excision. Long-term follow-up with your dermatologist is still important, as new LM lesions can develop in adjacent sun-damaged skin.

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  2. Bricca GM, Brodland DG, Ren D, Zitelli JA. Cutaneous head and neck melanoma treated with Mohs micrographic surgery. J Am Acad Dermatol. 2005;52(1):92-100.
  3. Zalla MJ, Lim KK, Dicaudo DJ, Gagnot MM. Mohs micrographic excision of melanoma using immunostains. Dermatol Surg. 2000;26(8):771-784.
  4. Connolly SM, et al. AAD/ACMS/ASDSA/ASMS appropriate use criteria. J Am Acad Dermatol. 2012;67(4):531-550.
  5. Hazan C, Dusza SW, Delgado R, et al. Staged excision for lentigo maligna and lentigo maligna melanoma. J Am Acad Dermatol. 2008;58(1):142-148.

Trusted Resources

Always consult a board-certified dermatologist or Mohs surgeon for diagnosis and treatment recommendations specific to your situation.