Positive Margins & Frozen Section in Oral Cancer Surgery

When oral cancer is operated on, the aim is to remove the whole tumour together with a cuff of healthy tissue around it. That cuff is the surgical margin, and the words clear, close and positive in your report describe how wide it was under the microscope. Margin status is one of the main things that decides whether you need more treatment after surgery.

This guide covers how margins are measured, why shrinkage matters, how a frozen section during surgery works, and what usually follows if a margin is close or positive. It is general information. Your own plan depends on your full report and your treating team.

What are surgical margins?

In a wide local excision for oral cavity cancer, the surgeon cuts through healthy-looking tissue some distance from the visible tumour. This is needed because cancer can send microscopic extensions into muscle, lining and along nerves beyond what can be seen or felt.

After removal, the pathologist paints the cut surfaces with coloured ink, so that each side (front, back, top, bottom, deep) can be identified. The tissue is cut across and the distance between the tumour and the inked edge is measured under the microscope. For help reading the rest of the report, see our guide to the oral cancer histopathology report.

How margins are classified

Guidelines such as those from the National Comprehensive Cancer Network (NCCN) and the College of American Pathologists use broadly similar categories.

Exact cut-offs differ a little between laboratories. Ask your surgeon how your report defines each category, and what the actual measurement in millimetres was.

The 5 mm figure and tissue shrinkage

Several mostly retrospective studies link margins of 5 mm or more with lower local recurrence, which is why this figure is widely used. There is a catch that families rarely hear about: tissue shrinks.

1. In the mouth: surgeons commonly aim for about 1 cm of normal-looking tissue around the tumour.
2. Elastic recoil: muscle tone and elastic fibres pull the specimen in as soon as it is cut free.
3. Formalin fixation: preserving the specimen for the laboratory shrinks it further.

Studies report combined shrinkage over a wide range, often cited as around 25 to 50 percent depending on the site and technique. So a 10 mm margin in the mouth can measure around 5 to 7 mm, or less, on the slide. This is why the planned margin is wider than the number in the report.

What is an intraoperative frozen section?

Waiting a week to learn that tumour was left behind may mean another operation. To lower that chance, surgeons often use a frozen section, a quick pathology check done while you are still under anaesthesia.

How it works

1. The surgeon removes the tumour with the intended margin.
2. Small strips are taken from the edges of the specimen, or from the wound bed in the mouth, and labelled by site.
3. They go straight to the pathology laboratory.
4. The pathologist freezes the tissue so it can be sliced thinly, stains it and examines it under the microscope.
5. The result is phoned to the operating theatre, usually in about 20 to 30 minutes, as clear, positive or showing abnormal cells (dysplasia).

If a particular edge, for example the deep muscle or the back mucosal edge, shows tumour, the surgeons return to that area and remove more tissue, and may send another sample. This is called re-excision of the margin.

Frozen section helps but has limits. Only selected areas are sampled, bone and calcified tissue cannot be frozen well, and freezing distorts cells. Some studies also suggest that a margin made clear by re-cutting may not carry quite the same low risk as one that was clear first time. That is why the first cut is planned generously, and why the final report still matters.

Free flap reconstruction, such as a fibula free flap done with a reconstructive colleague, is generally carried out after the margins have been assessed, because covering the area with a flap makes it much harder to go back and remove more tissue.

Why the final report can differ from the frozen section

It can be very confusing when the surgeon says the frozen sections were clear and a week later the final report mentions a close or positive margin. Published studies generally show good agreement between the two, but differences can happen for real reasons.

Different processing. Frozen tissue forms ice crystals that distort cell detail, so subtle abnormal cells, small tumour islands or high-grade dysplasia are easier to miss. The final slides are made from tissue fixed in formalin, embedded in wax and stained after careful processing, which gives finer detail.

Sampling. The whole wound cannot be frozen, so a small cluster of cells lying between two sampled spots may only appear on the final report, which examines far more of the specimen.

Shrinkage. A margin that measured just over 5 mm when fresh may measure under 5 mm after fixation, moving the report from "clear" to "close".

Why close or positive margins happen

Surgeons aim for wide margins, but the head and neck is crowded. Tumours of the tongue, floor of mouth and back of the mouth lie close to the carotid vessels, the pterygoid muscles and skull base, and nerves that control tongue movement and feeling. When a tumour touches such a structure, taking another centimetre may not be safe. The surgeon removes as much as can be done safely, and the team plans further treatment from the final report.

Some cancers are also biologically harder to clear. They may spread along nerves (perineural invasion), enter tiny vessels (lymphovascular invasion) or grow as small scattered cords and single cells rather than a solid block.

Told your margins are close or positive? Dr. Pradeep S. and Dr. Kalpa Pandya see patients at Apollo Main Hospital, Greams Road, Chennai. Book a consultation or call +91 96633 03747 to have your pathology report and operation notes reviewed and the next steps explained.

Why margins matter for the future

Margin status is an important factor in the chance of the cancer coming back in the mouth. Studies consistently link clear margins with lower local recurrence, and positive margins with a clearly higher one. The reported figures vary widely between series, so they should not be read as a personal forecast. Recurrence in a previously operated and sometimes irradiated area is harder to treat because of scarring and altered blood supply, and that is why so much attention goes to getting the first operation right. Our guide to recurrence signs and follow-up explains what to watch for afterwards.

A close or positive margin does not mean that treatment has failed. It is information that tells the team what to do next.

What happens if the final report shows a close or positive margin

The plan depends on which margin is involved, how much, and what else the report shows (perineural invasion, lymphovascular invasion, nodal disease and extranodal extension). The usual options, in line with guidelines such as NCCN, are these.

1. Further surgery (re-excision)

If the involved area can be safely reached, for example a superficial mucosal edge of the cheek or lip, and no flap has made it difficult, a second operation to remove more tissue may be advised. Where possible this is preferred, because the aim is to convert a positive margin into a clear one.

2. Post-operative radiation

If more surgery is not possible, for example when the margin is against the skull base or deep beneath a reconstruction, or when other risk features are present, radiation to the surgical bed is usually recommended. It is planned and given by radiation oncologists, and generally begins within about six weeks of surgery once healing allows. Our article on radiation or chemo after oral cancer surgery covers what to expect.

3. Chemoradiation

A positive margin and extranodal extension in neck nodes are the two classic high-risk features for which adding chemotherapy (usually cisplatin, given by medical oncologists) to radiation is considered. A combined analysis of two large trials, EORTC 22931 and RTOG 9501, found that adding chemotherapy improved outcomes in people with these features, at the cost of more side effects. Whether it suits you depends on your age, kidney function and general health.

Questions to ask your surgeon

1. What were my margins in millimetres on the final report, and which sites were closest?
2. Was a frozen section done, and what did it show?
3. If a margin is close or positive, is more surgery possible, or is radiation the better route?
4. Does my report show perineural invasion, lymphovascular invasion or extranodal extension?
5. Has my case been discussed at a multidisciplinary tumour board?

Seeing the surgeons in Chennai

Dr. Pradeep S. (MDS, FHNS, FIBCSOMS, PGDCR) is an oral and maxillofacial surgeon with a head and neck surgical oncology fellowship from HCG Manavata Cancer Centre, Nashik, and more than 15 years' experience in oral, head and neck cancer surgery, including three years in head and neck oncology at Apollo Proton Cancer Centre. Dr. Kalpa Pandya (BDS, MDS, FHNS) is an oral and maxillofacial surgeon who also holds a head and neck oncology fellowship. They see patients at Apollo Main Hospital, Greams Road, Chennai, and review scans and pathology together with radiation and medical oncology colleagues, who plan any radiation or chemotherapy.

If you have been told your margins are close or positive and want a surgical opinion, see our second opinion service or book an appointment. You can also call +91 96633 03747.

References

1. National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Head and Neck Cancers (current version), nccn.org.
2. Bernier, J., et al. "Postoperative irradiation with or without concomitant chemotherapy for locally advanced head and neck cancer." New England Journal of Medicine, 2004; and Bernier, J., et al. "Defining risk levels in locally advanced head and neck cancers: a comparative analysis of concurrent postoperative radiation plus chemotherapy trials of the EORTC (#22931) and RTOG (#9501)." Head & Neck, 2005.
3. Brandwein-Gensler, M., et al. "Validation of the histologic risk model in a new cohort of patients with head and neck squamous cell carcinoma." American Journal of Surgical Pathology, 2010.
4. WHO Classification of Tumours Editorial Board. Head and Neck Tumours, 5th ed. IARC, 2022.