When Mohs surgery is the right choice, even when the cancer is not on your face
Almost everyone believes Mohs surgery is a face procedure. Patients believe it, and it is not unusual for the belief to travel with a referral. It is an understandable assumption, because the face is where Mohs is used most often. But it is the wrong mental model, and it quietly costs people.
The cost runs in one direction. A tumor on the face that would do fine with a simpler treatment occasionally gets more procedure than it needed. That is a real inefficiency, and I will come back to it. The more common and more expensive error runs the other way: a tumor on a hand, a shin, an ear, or a scalp that genuinely warranted complete margin control gets something less, because it was not on a face and nobody asked the next question.
Here is the next question, and what actually answers it.
Mohs is a way of reading the margin, not a place on the body
The distinguishing feature of Mohs micrographic surgery is not where it happens or how carefully the surgeon cuts. It is that one hundred percent of the surgical margin is examined under a microscope during your appointment, rather than a small sample of it being read days later.
Standard excision slices the specimen across like a loaf of bread and examines those slices, which samples well under one percent of the true margin. The rest is inference. Mohs lays the entire outer surface flat and reads all of it, the way you would peel the wrapper off a Reese’s cup and lay it on a slide. I have explained that difference at length in the basal cell carcinoma article, and what the day itself is like in the hour-by-hour walkthrough.
Once you see it that way, the real question stops being where is the tumor and becomes how much does it matter that we know exactly where this tumor ends? The face makes that matter a great deal, because tissue there is scarce and irreplaceable. But the face is not the only thing that makes it matter.
The part that surprises people: the advantage grows as the tumor gets harder
Most people carry an intuition that goes roughly: for a straightforward tumor you use the precise technique, and for a difficult one you need a bigger, more aggressive operation. It is a reasonable instinct and it is backwards.
The pooled analyses that established Mohs’ role reported recurrence rates across many categories of tumor, and the pattern is consistent: the harder the tumor, the wider the gap.
| Situation | Mohs | Other treatments |
|---|---|---|
| Basal cell carcinoma, never treated before | ~1% | ~10% (standard excision) [1] |
| Basal cell carcinoma that has already come back once | 5.6% | 19.9% overall; 17.4% excision; 40% ED&C [2] |
| Squamous cell carcinoma of skin and lip, never treated before | 3.1% | 10.9% [3] |
| Squamous cell carcinoma of the ear | 5.3% | 18.7% [3] |
| Squamous cell carcinoma larger than 2 cm | 25.2% | 41.7% [3] |
| Squamous cell carcinoma that has already come back once | 10% | 23.3% [3] |
| Squamous cell carcinoma growing along nerves | 0% | 47% [3] |
Look at the last row. Tumors growing along nerves recurred in nearly half of cases with conventional treatment and in none of the Mohs cases in that analysis. [3] Look at the second row: a basal cell carcinoma that has already come back once, treated again with scrape and burn, recurred forty percent of the time. The authors of that analysis stated the conclusion directly, that ED&C should not be used to treat a recurrent basal cell carcinoma at all. [2]
None of those rows says anything about the face.
What actually drives the decision
Formal appropriate use criteria exist for exactly this question, developed jointly by several dermatology and surgical societies. [4] They weigh location alongside size, growth pattern under the microscope, patient factors, and whether the tumor has been treated before.
Location is sorted into three areas, and this is where the face myth quietly falls apart. Area H, the group where tissue conservation is considered critical, contains several places that are nowhere near a face. Area M is also an indication on its own. Only Area L, the trunk and the limbs, waits on something else about the tumor.
Those inputs fall into three groups, and it is worth holding them apart: what kind of tumor it is, who you are, and where it sits. Most patients only ever hear about the third.
| Area | Where | What it means |
|---|---|---|
| H | Eyelids, eyebrows, nose, lips, chin, ears, in front of and behind the ears, temples, genitalia, hands, feet, ankles, and the areola | Tissue conservation is critical here. |
| M | Cheeks, forehead, scalp, neck, jawline, and the shin | Mohs is indicated for tumors in these locations. |
| L | Trunk and extremities | Mohs is indicated for larger tumors, or tumors with aggressive features under the microscope. |
Start with the tumor.
The growth pattern on your pathology report
Some skin cancers grow as a reasonably contained mass. Others send out fine strands well beyond anything visible on the surface, so the tumor underneath is meaningfully wider than the spot. Words like infiltrative, morpheaform, sclerosing, or micronodular on a pathology report signal that pattern. So does basosquamous, which describes a basal cell carcinoma carrying features of squamous cell carcinoma and behaving more aggressively than an ordinary one. Less common descriptions carry weight too: spindle cell, sarcomatoid, small cell, clear cell, acantholytic, and pagetoid patterns are all harder to predict and harder to see the edges of. So is a tumor described as moderately or poorly differentiated, meaning the cells have drifted further from what normal skin cells look like, or as deeply infiltrating. These are the tumors where an estimated margin is most likely to be wrong, because there is genuinely more tumor than the eye can find.
There is a wrinkle worth knowing. A study reviewing tumors removed by Mohs found that aggressive subtypes needed more than one stage far more often than non-aggressive ones, which is expected. But it also found that once the full specimen was examined, mixed histologic types were more common than generally assumed, and the authors concluded that surgeons should not place too much confidence in the subtype identified on the initial biopsy. [5] A biopsy samples a fragment. The tumor is entitled to be more complicated than the fragment suggested. (If you are holding a report and want help with the words on it, see how to read a pathology report.)
The tumor has been treated before
A recurrent tumor is a different problem from a new one, for two reasons. It has already demonstrated that it can survive a treatment, which is information about that specific tumor. And the previous treatment left scar tissue, which obscures the borders and makes any estimate of where the tumor ends less reliable than it was the first time.
This is the single clearest case in the table above, and it applies anywhere on the body.
Size, nerve involvement, and how the cells look
For squamous cell carcinoma in particular, crossing about 2 cm across changes the risk category, as does growth along nerves and a poorly differentiated appearance under the microscope. I have covered why size matters in both directions in the squamous cell carcinoma article. A 3 cm tumor on a forearm is not a low-risk tumor because a forearm is not a face.
Depth counts as well, whether it was measured or only suspected, and it may be written on your report in more than one way. A Breslow depth of 2 mm or more and a Clark level of IV or greater are two ways of saying the same thing: the tumor has reached further down than the surface suggested. That 2 mm is not an arbitrary line. It is the same threshold described in the squamous cell carcinoma article, below which a study of 615 patients saw no spread at all, and above which the risk becomes real. [9]
The margin came back positive
This one is common and deserves its own line. If a tumor was excised and the pathology report says the margin was positive, cancer was left behind. You are now dealing with a tumor whose remaining edges sit inside fresh scar tissue, which is precisely the situation where estimating a border is least reliable.
How fast it grew, and how long it has been there
Both ends of that range matter, for opposite reasons. A rapidly growing tumor is telling you something about its biology, and it is unlikely to have stopped growing between the biopsy and the surgery. A tumor of long-standing duration, the spot that has been there for years and was assumed to be nothing, has had time to extend well past what anyone can see.
Field cancerization
Sometimes the problem is not one tumor but the neighborhood it grew in. When an area has taken enough ultraviolet damage, the surrounding skin is not innocent bystander tissue. It is skin that has accumulated the same mutations and is producing abnormal cells across the whole region. This is called field cancerization, and it is why a bald scalp or a forearm can generate one tumor after another in the same few square inches. It also means the visible edge of any single tumor is a less meaningful boundary than usual.
Borders nobody can define by looking
Some tumors have a clean, obvious edge. Others fade into surrounding sun-damaged skin with no clear boundary anywhere. When the honest answer to “where does this end” is “I cannot tell you by looking,” that is precisely the circumstance where reading the whole margin earns its cost.
Some of it is not about the tumor at all
This is the half of the decision patients almost never hear about, and several of the items below point toward complete margin control largely on their own, whatever the tumor looks like and wherever it happens to be.
A suppressed immune system
Transplant recipients and others on long-term immunosuppression develop more skin cancers, and those cancers tend to behave more aggressively. The stakes of leaving a margin behind are higher in someone whose immune system will not be helping.
Worth naming specifically, because patients often do not think of these as relevant to their skin:
- Any systemic immunosuppressant medication, whether for a transplant, an autoimmune disease, or an inflammatory condition.
- Chronic kidney disease and renal failure.
- A history of leukemia, and chronic lymphocytic leukemia in particular, along with lymphoma. These matter even when the blood condition is stable and being watched rather than treated.
- HIV.
If any of these apply to you, say so at the visit even if nobody asks. It is the kind of history that sits in a different part of your chart and does not always travel with a skin referral.
A cancer that started in a scar, a burn, or a wound that never healed
Skin cancers can arise in skin that was injured long ago in some entirely different way. Old burn scars, chronic ulcers, sinus tracts, long-standing pressure sores, sites of chronic bone infection, and previously irradiated skin can all give rise to a cancer years or decades later. [6] The old name for this is a Marjolin’s ulcer.
It matters here for two reasons. These tumors do not necessarily behave like an ordinary sun-related skin cancer. And the scar itself obscures the border, so an estimate of where the tumor ends is less reliable exactly where you would most want it to be reliable.
There is a practical instruction buried in this. A wound that has not healed in months deserves a biopsy rather than another dressing. The assumption that a long-standing sore is just a stubborn wound is how these are missed.
Skin that has been irradiated before
If you had radiation to an area years ago, whether for a previous skin cancer or for something unrelated, a tumor that later appears in that field is treated as higher risk. Irradiated skin also heals less well, so taking a generous margin costs more there than it would elsewhere. Both facts push in the same direction.
Inherited conditions
Some people are not dealing with a skin cancer. They are dealing with a condition that will keep producing them, and that changes the arithmetic completely.
- Gorlin syndrome, also called basal cell nevus syndrome, comes from a mutation in the PTCH1 gene and produces basal cell carcinomas often starting in adolescence, alongside jaw cysts, rib abnormalities, and pits on the palms and soles. [7] Someone facing a lifetime of tumors cannot afford a generous margin on each one. Tissue spent at thirty is not available at sixty.
- Xeroderma pigmentosum is an inherited condition in which the machinery that repairs ultraviolet damage to DNA does not work properly, so cancers begin in childhood and keep coming. [8]
- Others exist, and they are worth mentioning to your dermatologist even if the connection seems far-fetched: a parent who had dozens of skin cancers, unusual jaw cysts, severe sunburns in early childhood, or skin cancers in the family at unusually young ages.
One specific point worth acting on: a basal cell carcinoma in an adolescent or young adult should prompt an evaluation for basal cell nevus syndrome. [7] If that is you or your child, say so out loud rather than assuming someone has noticed.
A long history of skin cancers
This one is not a syndrome. It is arithmetic.
Someone on their fifteenth skin cancer is in a different position from someone on their first, even when this particular tumor is entirely unremarkable. Every removal spends tissue that does not grow back, and the spending accumulates across a lifetime. At some point tissue conservation stops being about appearance and starts determining whether the next tumor can be closed at all, or whether the area still has enough healthy skin left to work with.
If you have had many skin cancers, that history is itself a reason to ask about margin control, even for a tumor that would be unremarkable in someone having their first.
Two related patterns count for the same reason. A historical trend of aggressive skin cancers, meaning yours have repeatedly turned out worse under the microscope than they looked on the surface, is information about how your skin behaves. So is a historical trend of difficulty: tumors that have needed more than one attempt, come back after treatment, or turned out larger than expected once surgery began. If that has been your experience more than once, it is not bad luck, and it belongs in the plan for the next one.
Places on the body where tissue is not spare
The reason the face dominates this conversation is that facial tissue is scarce, visible, and functional. Take a centimeter too much beside an eyelid and you have created a second problem.
But the face is not the only place where that is true.
- Hands and fingers. There is very little spare skin, and what is there has to keep moving. Extra margin taken here is paid for in stiffness and function, not just appearance.
- The areola. Listed alongside the eyelid and the lip, and almost nobody expects it to be.
- Feet and ankles. Skin is under mechanical load with every step and healing is slower.
- Shins and the lower legs. This one is underestimated constantly. Circulation is poorer, healing is slower, and there is very little loose skin to close a defect with. A wound here that would have been minor on a back can take months.
- Genitalia. Scarce tissue, functional consequences, and a location where people delay seeking care to begin with.
- Ears and scalp. Technically not the face, routinely treated as though the rules are different there, and they are not.
The principle underneath all of these is the same one that makes Mohs valuable on a nose. When there is no spare tissue, the value of taking only what is actually cancerous goes up, because every extra millimeter of normal skin removed is a millimeter that has to come from somewhere, or be closed under tension, or be left to heal on its own.
The full list, for anyone holding a pathology report
Everything above is the reasoning. What follows is the working inventory, drawn from the national cancer guidelines that define high-risk and very-high-risk squamous cell carcinoma [10] together with the appropriate use criteria. [4] It is more useful than a summary if you have a report in front of you and want to know whether anything on it is doing work.
You do not need all of these. One is often enough.
Aggressive features under the microscope
| On the report | What it means |
|---|---|
| Infiltrative, morpheaform, sclerosing, micronodular | Growth in fine strands that run beyond the visible edge |
| Basosquamous | A basal cell carcinoma with squamous features; behaves more aggressively than an ordinary one |
| Spindle cell, sarcomatoid, small cell, clear cell, acantholytic, pagetoid | Less common patterns that are harder to predict and harder to trace to an edge |
| Moderately differentiated, poorly differentiated | The cells have drifted further from normal |
| Perineural invasion | Tumor traveling along a nerve, which is a route out of the visible area |
| Deeply infiltrating, or suspected deep tissue invasion | Depth the surface does not reveal |
| Breslow depth 2 mm or greater; Clark level IV or greater | Two ways of recording how deep the tumor reached; 2 mm is the threshold where the risk of spread starts |
Complicating features of the tumor or the site
| Feature | What it means |
|---|---|
| Positive margin on a previous excision | Cancer was left behind, and its edges now sit in scar |
| Recurrent tumor | It has already survived one treatment |
| Large size | More edge to get wrong, and a higher-risk category once past about 2 cm |
| Poorly defined clinical borders | Nobody can say by looking where it ends |
| Rapidly growing | Biology that is unlikely to have paused since the biopsy |
| Long-standing duration | Years of quiet extension past the visible spot |
| A location with a high recurrence rate | Some sites simply fail more often |
| An area critical for tissue conservation | There is no spare skin to give away |
| Chronic ulceration or inflammation | Long-irritated skin, with borders hidden in damaged tissue |
| Osteomyelitis at the site | Chronic bone infection, with the same problem |
| A traumatic scar | A cancer arising in an old injury; the scar hides the edge |
| Prior radiation to the area | Higher risk in that field, and skin that heals poorly |
| Field cancerization | The surrounding skin is damaged too, so the edge means less |
| Basal cell nevus syndrome (Gorlin) | A lifetime of tumors; tissue must be conserved every time |
| Xeroderma pigmentosum | Defective repair of ultraviolet damage; cancers from childhood |
Features of the patient
| Factor | What it means |
|---|---|
| Systemic immunosuppressant medication | Including for transplant, autoimmune, and inflammatory conditions |
| Renal failure | Immune function is affected even without medication |
| Leukemia, including CLL; lymphoma | Counts even when stable and only being monitored |
| HIV | |
| A historical trend of aggressive skin cancers | Yours have repeatedly been worse under the microscope than they looked |
| A historical trend of difficulty with skin cancers | Yours have needed repeat attempts, come back, or proved larger than expected |
When Mohs is not the answer
An article arguing that Mohs is under-used elsewhere would be dishonest if it did not say plainly where it is unnecessary, so here it is.
A small, ordinary, previously untreated basal cell carcinoma with a non-aggressive growth pattern, sitting on a back or a shoulder where there is plenty of skin, does not need Mohs. A standard excision handles it, and the extra margin costs nothing that matters in that location. Mohs takes several hours, costs more, and uses resources that another patient may need more. Choosing it for a tumor that does not require it is not a harmless bit of extra caution.
The point of this article is not that Mohs is always better. It is that “it is not on my face” is not the reason to rule it out, because location is one factor among at least half a dozen, and the other factors do not stop applying below the neck.
What to ask
If you have been told you need a skin cancer removed and you would like to understand the plan, these are reasonable and specific questions:
- What growth pattern did the biopsy show? The answer is on the pathology report.
- Has this spot been treated before? Including anything frozen, burned, or creamed years ago that you may not think of as treatment.
- How will the margins be checked, and when will we know? During the appointment, or days later from a lab.
- How much normal skin are we planning to take, and how will this close? Particularly on a hand, a shin, or an ankle.
- Does anything in my history change this? Scars, burns, or old wounds at the site, previous radiation to the area, a suppressed immune system, a lot of prior skin cancers, or skin cancers in the family at young ages.
None of these are challenges to your physician, and none of them require you to have an opinion about the answer. They are the questions that surface the factors this decision actually turns on.
The bottom line
Mohs surgery is used most often on the face because the face has the least spare tissue and the most visible consequences. That is a good reason, and it has hardened into a bad rule.
The technique is a way of knowing exactly where a tumor ends. How much that knowledge is worth depends on how unpredictable the tumor is and how expensive the surrounding tissue is, and both of those vary enormously across a body. A recurrent tumor on a shin, an infiltrative one on a forearm, or a large one on an ear can all have a stronger claim on complete margin control than a small, well-behaved tumor on a cheek.
Ask what kind of tumor you have and what else about you belongs in the decision, not just where it is.
References
- Rowe DE, Carroll RJ, Day CL Jr. Long-term recurrence rates in previously untreated (primary) basal cell carcinoma: implications for patient follow-up. J Dermatol Surg Oncol. 1989;15(3):315-328. doi:10.1111/j.1524-4725.1989.tb03166.x
- Rowe DE, Carroll RJ, Day CL Jr. Mohs surgery is the treatment of choice for recurrent (previously treated) basal cell carcinoma. J Dermatol Surg Oncol. 1989;15(4):424-431. doi:10.1111/j.1524-4725.1989.tb03249.x
- Rowe DE, Carroll RJ, Day CL Jr. Prognostic factors for local recurrence, metastasis, and survival rates in squamous cell carcinoma of the skin, ear, and lip. Implications for treatment modality selection. J Am Acad Dermatol. 1992;26(6):976-990. doi:10.1016/0190-9622(92)70144-5
- Connolly SM, Baker DR, Coldiron BM, et al. AAD/ACMS/ASDSA/ASMS 2012 appropriate use criteria for Mohs micrographic surgery. J Am Acad Dermatol. 2012;67(4):531-550. doi:10.1016/j.jaad.2012.06.009
- Ro KW, Seo SH, Son SW, Kim IH. Subclinical infiltration of basal cell carcinoma in Asian patients: assessment after Mohs micrographic surgery. Ann Dermatol. 2011;23(3):276-281. doi:10.5021/ad.2011.23.3.276
- Meaume S, Fromantin I, Teot L. Neoplastic wounds and degenerescence. J Tissue Viability. 2013;22(4):122-130. doi:10.1016/j.jtv.2013.07.001
- Lam C, Ou JC, Billingsley EM. “PTCH”-ing it together: a basal cell nevus syndrome review. Dermatol Surg. 2013;39(11):1557-1572. doi:10.1111/dsu.12241
- Mareddy S, Reddy J, Babu S, Balan P. Xeroderma pigmentosum: man deprived of his right to light. ScientificWorldJournal. 2013;2013:534752. doi:10.1155/2013/534752
- Brantsch KD, Meisner C, Schönfisch B, et al. Analysis of risk factors determining prognosis of cutaneous squamous-cell carcinoma: a prospective study. Lancet Oncol. 2008;9(8):713-720. doi:10.1016/S1470-2045(08)70178-5
- National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Squamous Cell Skin Cancer; Basal Cell Skin Cancer. NCCN.org.
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Medical content: William S. Farmer, MD · Last reviewed: July 2026
