How Both Treatments Work
Skin cancer is treated by surgically removing the tumor along with a border (margin) of normal-looking tissue around it. The goal of this margin is to make sure no cancer cells are left behind at the edges. Both Mohs surgery and standard excision accomplish this goal, but they differ in how thoroughly the margins are checked, how quickly results are known, and how much tissue needs to be removed to achieve a clear margin.
Standard Excision
In standard excision, your surgeon removes the tumor with a preset margin of normal skin, for example, 4 mm for low-risk basal cell carcinoma (a common type of skin cancer). The removed tissue is sent to a separate pathology lab, where a technician prepares it using a process called bread-loaf sectioning. In this method, the tissue is sliced into thin cross-sections, like slices of bread. These slices represent only about 1–2% of the actual wound edge. Results come back in 1–5 business days. If the margins come back positive (meaning cancer is still present at the edge), a second surgery is needed to remove more tissue.
Mohs Micrographic Surgery
In Mohs surgery, your surgeon removes the tumor one thin layer at a time and personally examines every millimeter of the wound edge under a microscope. Right in the office, the same day. This is possible because the tissue is processed using a special horizontal (flat) cutting technique that maps the entire edge. If cancer is still present at any edge, the surgeon removes only that specific area and repeats the examination. This continues until the entire margin is clear. Because the entire edge is examined rather than a small sample, the method is far more thorough. And because it happens in real time, no second appointment is needed.
Side-by-Side Comparison
The table below compares Mohs surgery and standard excision across the features that matter most to patients. Keep in mind that both are accepted, evidence-based treatments. The right choice depends on your individual situation.
| Feature | Mohs Surgery | Standard Excision |
|---|---|---|
| Cure rate (primary BCC) | ~99% | ~93–95% |
| Margin examination | ~100% of wound edge examined | ~1–2% of wound edge sampled |
| Tissue preservation | Excellent. Only cancerous areas removed | Good. Standard preset margin used throughout |
| Results known | Same day, in real time | 1–5 business days after surgery |
| Number of visits | Usually one (surgery + repair same day) | Usually two (surgery + separate results appointment) |
| Where performed | Mohs surgeon's office or specialized clinic | Dermatologist's office, surgery center, or hospital |
| Anesthesia | Local (numbing injection. You stay awake) | Local; general anesthesia sometimes used for larger excisions |
| Typical duration | 2–4+ hours (includes lab waiting time between stages) | 30–60 minutes (lab results take several days) |
| Best suited for | High-risk tumors; facial or functionally critical locations; recurrent cancers | Low-risk tumors; locations where tissue conservation is less critical; simple, well-defined cancers |
| Cost and access | Higher cost; requires a specially trained Mohs surgeon | Lower cost; widely available from general dermatologists and surgeons |
When Your Doctor May Recommend Mohs Surgery
Mohs surgery is not needed for every skin cancer. It is recommended when the clinical situation calls for either the highest possible cure rate or the most tissue conservation, or both. Your doctor uses guidelines from dermatology and oncology organizations, as well as their own clinical experience, to decide whether Mohs is the right fit.
Helpful Tips
- Location on the face, especially around the eyes, nose, lips, or ears. These areas have little extra skin to spare, and recurrence in these areas is particularly difficult to treat.
- Recurrent cancer. A tumor that has come back after being treated before. Recurrent cancers tend to have hidden extensions that standard excision can miss.
- Aggressive tumor type. Some subtypes of basal cell carcinoma (such as morpheaform or infiltrative) or squamous cell carcinoma (poorly differentiated or with nerve involvement) have irregular, finger-like extensions that are hard to predict from the surface.
- Unclear borders. Tumors whose edges are hard to see on the skin surface.
- Large tumor size relative to the location.
- Patients who are immunosuppressed (have a weakened immune system), since their skin cancers tend to behave more aggressively.
- Locations where preserving maximum tissue affects function, such as the eyelid, lips, or fingers.
When Standard Excision May Be the Right Choice
Standard excision is an excellent treatment for many skin cancers, and it has decades of evidence supporting its safety and effectiveness. It is a simpler procedure that is available from a wider range of doctors, which can be an advantage in terms of scheduling and access to care.
Helpful Tips
- Small, low-risk basal cell carcinoma on the trunk or limbs. These tumors have a low chance of incomplete removal with standard margins.
- Squamous cell carcinoma in situ (Bowen's disease). This early form of SCC has not yet grown deep into the skin and is well-managed with excision.
- Well-defined tumors with clear borders in locations where tissue conservation is less critical.
- Patients for whom a Mohs-trained surgeon is not accessible or the added precision of Mohs is not clinically necessary.
- Tumors that are part of a larger surgical procedure already being performed under general anesthesia.
Understanding Cure Rates
Cure rate numbers can sound abstract. Here is what they mean in practical terms. For primary (first-time, never treated) basal cell carcinoma, Mohs surgery cures approximately 99 out of 100 cases. Standard excision cures approximately 93–95 out of 100 cases. This means that for every 100 patients treated, standard excision leaves 5–7 patients with residual cancer that will need further treatment, compared to roughly 1 patient with Mohs. For recurrent basal cell carcinoma (cancer that has come back after prior treatment), the gap is even wider. Mohs achieves roughly 95% cure, while standard re-excision achieves closer to 80%. These differences are the main reason Mohs is preferred for high-risk situations.
Helpful Tips
- Cure rates are population averages. Your individual result depends on your tumor's specific features, not just these numbers.
- Even if standard excision is used and margins come back positive, the situation is manageable: a second surgery can clear the remaining tumor.
- Ask your doctor which cure rate applies more closely to your specific cancer type and situation.
The Bottom Line: Both Are Effective Treatments
It is important to understand that both Mohs surgery and standard excision are legitimate, well-studied, and widely accepted treatments for skin cancer. Neither approach is universally superior. Each has strengths that make it the better choice for specific situations. Your dermatologist has recommended the approach that is best matched to your cancer's type, location, size, and risk profile, as well as your personal health and access to care. If you have questions about why one approach was recommended for you over the other, your doctor is always the right person to ask. There are no wrong questions.
Helpful Tips
- If you are unsure about the recommendation, a second opinion from another dermatologist or Mohs surgeon is always a reasonable option.
- Whichever treatment you receive, following your wound care instructions closely is one of the most important things you can do to help healing go smoothly.