# Mohs surgery

Source: https://onco.cc/terms/mohs-surgery/  
OnCo record `mohs-surgery` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Skin cancer surgery in which the tumour is removed in thin layers, each checked under the microscope on the spot, until the edges are clear; it spares the most normal skin.

## Summary

Developed by Frederic Mohs, it achieves cure rates above 97% for basal cell and cutaneous squamous cell carcinomas, and is preferred for tumours on the face, recurrent tumours, and aggressive histologies where tissue conservation matters. Each stage takes an hour or so of processing, so the procedure can last a day. It is not used for melanoma in most centres because frozen sections read melanocytes poorly.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: Mohs; Mohs micrographic surgery

## Notes

- What the day is actually like, from the British Association of Dermatologists and British Society for Dermatological Surgery leaflet. You are awake throughout with local anaesthetic, which stings for less than 30 seconds. The surgeon marks and photographs the lesion, removes it with a rim of normal-looking skin, dresses the wound and sends you to a recovery bay. It can take up to three hours to get the result of one stage. If cancer remains, more anaesthetic is given and another stage is taken. In 90 percent of cases the cancer is gone after one or two stages, but you could be in hospital for up to a day, and the leaflet says in its own words that it can be a long and tiring day.
- The drawbacks the leaflet names itself, which are the ones worth hearing before asking for Mohs: waiting lists are usually longer than for standard excision because fewer cases fit into a day, which means the cancer could grow while you wait; the procedure takes longer on the day, half a day on average; more than one set of local anaesthetic injections is often needed; and not all skin cancers should be removed this way, because many are removed easily by standard excision with good outcomes.
- What the randomised evidence says it buys. In the Dutch trial of 408 primary and 204 recurrent high-risk facial basal cell carcinomas followed for ten years, cumulative recurrence was 4.4 percent after Mohs against 12.2 percent after surgical excision for primary tumours, which did not reach significance, and 3.9 percent against 13.5 percent for recurrent tumours, which did. The Cochrane review reads the same trial at three and five years (1.9 against 2.9 percent, and 3.2 against 5.2 percent) and grades the evidence low certainty, because the confidence intervals also include no difference.
- Practical arrangements the leaflet is specific about: you will need someone to drive you to and from the hospital, driving and public transport are not advised afterwards, you can eat and drink on the day unless told otherwise, and it is worth bringing something to do, a change of clothes and a list of your medicines and allergies.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Mohs_surgery
- Wikipedia: https://en.wikipedia.org/wiki/Mohs_surgery
- British Association of Dermatologists and British Society for Dermatological Surgery: Mohs micrographic surgery, patient information leaflet (updated June 2025): https://www.skinhealthinfo.org.uk/condition/mohs-micrographic-surgery/
- Cancer Research UK: Mohs micrographic surgery: https://www.cancerresearchuk.org/about-cancer/skin-cancer/treatment/surgery/mohs-micrographic-surgery-mms
- van Loo et al., surgical excision versus Mohs micrographic surgery for basal cell carcinoma of the face: randomised clinical trial with 10-year follow-up (Eur J Cancer 2014): https://doi.org/10.1016/j.ejca.2014.08.018
- Thomson et al., interventions for basal cell carcinoma of the skin: Cochrane review of 52 randomised trials and 6,690 participants (2020): https://doi.org/10.1002/14651858.CD003412.pub3

## Connected records

- terms: [Curettage and cautery](https://onco.cc/terms/curettage-and-cautery/), [Resection margins (R0 / R1 / R2)](https://onco.cc/terms/resection-margins/), [Skin grafts and flaps after skin cancer surgery](https://onco.cc/terms/skin-graft-and-flap-reconstruction/), [The growth pattern on a basal cell carcinoma report: nodular, superficial, infiltrative, basosquamous](https://onco.cc/terms/bcc-growth-pattern/), [The margin in skin cancer surgery](https://onco.cc/terms/surgical-margins-keratinocyte-cancer/), [The scar on the face after skin cancer surgery](https://onco.cc/terms/facial-scar-after-skin-cancer/), [What makes a skin cancer high risk: the UK feature lists](https://onco.cc/terms/skin-cancer-high-risk-features/), [Wide local excision](https://onco.cc/terms/wide-local-excision/)
- cancers: [Advanced cutaneous squamous cell carcinoma](https://onco.cc/cancers/advanced-cutaneous-scc/), [Basal cell carcinoma](https://onco.cc/cancers/basal-cell-carcinoma/), [Bowen's disease (squamous cell carcinoma in situ)](https://onco.cc/cancers/bowens-disease/), [Cutaneous squamous cell carcinoma](https://onco.cc/cancers/cutaneous-scc/), [Dermatofibrosarcoma protuberans](https://onco.cc/cancers/dermatofibrosarcoma-protuberans/), [Localised penile cancer (organ-confined, node-negative)](https://onco.cc/cancers/localised-penile-cancer/), [Locally advanced and metastatic basal cell carcinoma](https://onco.cc/cancers/locally-advanced-bcc/), [Penile cancer](https://onco.cc/cancers/penile/), [Skin cancer (all types)](https://onco.cc/cancers/skin-cancer/)
- fronts: [Surgery & Interventional](https://onco.cc/fronts/surgery/)
- trials: [Mohs surgery against ordinary excision for facial basal cell carcinoma (Maastricht trial)](https://onco.cc/trials/mohs-versus-excision-facial-bcc/), [VISMONEO (vismodegib before surgery for locally advanced basal cell carcinoma)](https://onco.cc/trials/vismoneo/)

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