Why does the math get harder with each Mohs site?

Mohs surgery is precise, but it is not fixed-time surgery. A single tumor may clear in one stage, or it may need two, three, or more. When two or three tumors are treated on the same day, the chance that at least one site needs another layer rises quickly.

A multicenter study by Rivera et al. found that 56% of tumors cleared in one Mohs stage 1 .

Modeled from Rivera et al.'s 56% one-stage clearance rate; assumes independent tumor behavior. Actual odds vary by tumor type, location, recurrence, surgeon, and patient factors.

That table is the whole lesson. With one tumor, there is a better-than-coin-flip chance of clearing in one stage. With three tumors, this simple model estimates an 82.4% chance that at least one site needs another layer.

Rivera et al. found that primary tumors averaged 2.25 hours, while recurrent tumors averaged 3.03 hours 1 . Alam et al. found mean stage counts of 1.92 for basal cell carcinoma and 1.66 for squamous cell carcinoma across 20 Mohs surgeons 2 .

So a three-site day is not just "one appointment instead of three." It can become a half-day or longer surgical day.

Why does longer surgery matter?

Longer surgery is not just inconvenient. It can change the risk profile. The REGESMOHS nationwide cohort of 5,017 Mohs patients identified duration of surgery as an independent risk factor for bleeding complications.

That matters because multiple sites can stretch the day in ways no one can fully predict before the first stage is processed 3 .

Blood thinners add another layer. Staging creates more separate surgery days. Combining sites creates one longer bleeding-risk window. The right answer depends on medication, tumor sites, expected repair, and why the patient takes the medication.

At Advanced Dermatologic Surgery, patients generally continue prescribed blood thinners unless the prescribing physician, cardiologist, or primary care clinician directs otherwise. A national survey found that therapeutic anticoagulants are rarely held, while practices vary more for preventive aspirin, NSAIDs, and supplements with anticoagulant effects 4 .

The point is not to scare patients. The point is to plan honestly. A shorter, more focused procedure often gives everyone more control.

Why do more wounds make recovery harder?

More sites mean more wounds, more dressings, more body positions, and more chances for wound-care mistakes. Mohs infection rates are usually low, but multiple simultaneous wounds make recovery more complicated.

The data are reassuring, but not zero-risk. In a 20,821-case multicenter study, Alam et al. found a very low overall adverse-event rate, but infection was the most common adverse event, accounting for 61% of adverse events 5 .

Schlager et al. found that local flaps carried 3.26 times the surgical-site infection risk and skin grafts carried 2.95 times the risk compared with simpler repairs 6 . Below-the-knee wounds deserve special respect. Patel et al. reported lower-extremity infection rates of 8.3% to 11.1% in a retrospective review 7 .

Chen et al. found that Mohs patients generally follow wound care well, with an average adherence score of 7.4 out of 8, but nonadherence was linked to feeling overwhelmed and wound-care discomfort 8 .

Now imagine a facial wound and a lower-leg wound on the same day. One is cosmetically sensitive. The other may require leg elevation, reduced activity, and careful swelling control. That is a lot to ask from a patient.

Why does reconstruction favor focus?

Reconstruction often decides the plan. When two skin cancers are close together, especially on the face, repairing one defect can change the tissue available for the next defect. One focused reconstruction often protects scar quality and surgical options.

Facial tissue is not unlimited. A flap for one defect can change tension lines, blood supply, tissue movement, and the options available for a nearby repair.

This does not mean reconstruction should be delayed casually. A large 2025 observational database study of facial Mohs reconstruction found that immediate reconstruction after a cleared Mohs defect was associated with lower wound dehiscence and lower revision rates compared with delayed reconstruction 9 .

The lesson is not "delay every repair." The lesson is to give each cleared defect the focused reconstruction plan it deserves.

Does local anesthetic have a limit?

Yes. Local anesthetic is very safe in Mohs surgery, but it has a ceiling. When several sites each need multiple stages and repeated injections, the cumulative dose becomes part of the planning.

AAD guidelines recommend a maximum dose of 7.0 mg/kg of lidocaine with epinephrine, with a practical ceiling of about 50 mL of 1% lidocaine, or 500 mg, over several hours for multistage procedures 10 .

The Mohs literature is reassuring. Alam et al. found serum lidocaine levels during Mohs surgery stayed far below toxic thresholds, even with volumes up to 48 mL 11 . Patrinely et al. reviewed 563 patients receiving more than 30 mL of lidocaine and found same-day complications in 1.4% 12 .

Those studies support the safety of local anesthesia. They do not mean planning can be ignored. One site per day gives the patient a fresh dose calculation and safety check each time.

When do I consider treating multiple sites the same day?

Same-day treatment of multiple sites may warrant consideration when there is a specific surgical reason, not just a scheduling reason. The decision should be individualized.

These are exceptions, not the default. The reason needs to be better than "it is more convenient."

Does this apply to standard excisions too?

Often, yes. Standard excision is more predictable than Mohs because there is no same-day microscopic stage processing, but multiple excisions still create multiple wounds, more anesthetic, more closure planning, and more wound-care instructions.

Standard excision is well established for appropriately selected basal cell carcinomas and low-risk cutaneous squamous cell carcinomas 13, 14 .

But the same practical questions apply: Are the wounds in different body regions? Will the repairs compete for nearby tissue? Will the patient have too many wound-care routines? Will a lower-leg wound make recovery harder? Will doing less today create a cleaner plan?

Sometimes less is more. That principle applies to Mohs surgery, standard excision, and any dermatologic surgery plan where the recovery burden matters as much as the schedule.

How does ADS approach multiple Mohs surgery sites?

Advanced Dermatologic Surgery generally favors one carefully planned surgery site at a time, while considering multi-site treatment when anatomy, reconstruction, travel, privacy, wound care, or patient-specific logistics justify a combined plan.

Dr. Hocker is a triple board-certified dermatologist, dermatopathologist, and Mohs micrographic surgeon at Advanced Dermatologic Surgery, a national referral center in Overland Park, Kansas for melanoma and high-risk skin cancer, advanced reconstructive plastic surgery, and advanced tissue diagnostics.

Dr. Hocker's triple board certification allows ADS to integrate surgical removal, refined reconstruction, and advanced laboratory studies on patients' tissue when clinically indicated.

For patients with more than one skin cancer, the goal is not simply to do more in one day. The goal is to choose the sequence that keeps cancer clearance first while protecting reconstruction, comfort, wound care, privacy, and the patient's real life.

Frequently Asked Questions

Bottom Line

When I stage Mohs surgeries across separate days, I am not being inefficient. I am choosing the plan that keeps cancer clearance first while protecting reconstruction, wound care, and recovery.

One site. One focused day. One clean result.