Oral cavity comprises the lips, buccal mucosa, teeth, gums, bony roof of the mouth, floor of the mouth, oral tongue, and retromolar trigone. The oral cavity structures have a rich lymphatic supply and about 30% of cases are diagnosed with a disease spread to lymph nodes (Level I to III). More than 90% of oral cavity cancers are SCCs. The ratio of incidences of oral cavity cancers reported in men and women is about 2:1, while the ratio is as high as 15:1 for lip cancers. The most common site of lip cancer is the lip vermilion (border of the lips and the facial skin).
Read about Risk Factors for Head and Neck cancer here.
Parts of Oral Cavity
Oral cavity comprises the lips, buccal mucosa, teeth, gums, bony roof of the mouth, floor of the mouth, oral tongue, and retromolar trigone. More than 90% of oral cavity cancers are squamous cell carcinoma. 
TNM Staging of Oral (Mouth) Cancer
TNM staging is the staging system used for oral cavity cancer. It is described as follows-
T STAGING
Tis – Carcinoma in situ or cancerous lesion is present only in the superficial layer of the oral cavity.
T1 – The primary tumor is </=2 cm in size and the depth of invasion (DOI) is </=5 mm. No spread to nearby lymph nodes or distant body parts. 
T2 – The primary tumor is </=2 cm in size with the DOI between 5 mm and 10 mm or primary tumor is >2 cm but </=4 cm with the DOI </=10 mm. 
T3 – The primary tumor is >4 cm in size with the DOI between 10 mm and 20 mm. 
T4a – The primary tumor invades adjacent structures and/or DOI > 20 mm. 
T4b – The primary tumor of any size that has invaded a vital structure, such as masticator space, pterygoid plates, skull base and/or surrounds the carotid artery. 
N STAGING
N0 – No spread of tumor to nearby lymph nodes
N1 – The disease has spread to a single ipsilateral lymph node measuring </=3 cm without extranodal involvement. 
N2a – The disease has spread to a single ipsilateral lymph node measuring >3 cm and </= 6 cm 
N2b – Metastasis to multiple ipsilateral nodes, none >6 cm 
N2c – Metastasis to bilateral/contralateral lymph nodes, all measuring <6 cm without extranodal involvement. 
N3 – The disease has spread to lymph nodes measuring >6 cm or extranodal involvement. 
M STAGING
M0 – No spread to distant body parts
M1 – Spread of the tumor to distant body parts.
4 Stages of Oral Cavity (Mouth) Cancer
Based on the TNM classification discussed above, oral cavity cancer is assigned a stage from I to IV.
| STAGE | TNM | ||
|---|---|---|---|
| 0 | Tis N0 M0 | ||
| I | T1 N0 M0 | ||
| II | T2 N0 M0 | ||
| III | T1-2 N1 M0 | ||
| T3 N0-1 M0 | |||
| IVA | T1-3 N2 M0 | ||
| T4a N0-2 M0 | |||
| IVB | Any T N3 M0 | ||
| T4b Any N M0 | |||
| IVC | Any T Any N M1 |
Survival Rate/ Life Expectancy of Oral Cavity (Mouth) Cancer
For Lip Cancer
5 year survival is as follows.
- Localised Disease- 92%.
- Regional Disease – 60%.
- Distant Disease – 28%.
For Tongue Cancer
5 year survival is as follows.
- Localised Disease- 81%.
- Regional Disease – 68%.
- Distant Disease – 39%.
For Floor of Mouth Cancer
5 year survival is as follows.
- Localised Disease- 77%.
- Regional Disease – 38%.
- Distant Disease – 20%.
Treatment of Oral Cavity (Mouth) Cancer
Stage 0
For Stage 0 cancers, surgical resection of the involved site is considered as the standard treatment. The patient should be followed-up closely after treatment for any sign of recurrence.
Stage I and II
For Stage I and II cancers, surgery is considered as the preferred treatment. Surgical resection of the involved site along with lymph node dissection is generally employed.therapy with or without chemotherapy may be employed after the primary treatment to kill any remaining cancer cells or in the presence of any adverse prognostic features. The patient should be followed-up closely after treatment for any sign of recurrence.
Stage III and IVA
For Stage III to IVA cancers, any of the following 3 approaches can be utilized as the preferred treatment: 1) Start treatment with chemotherapy (induction therapy) followed by radiation therapy or radiotherapy + chemotherapy based on the extent of tumor shrinkage with primary treatment. 2) Surgery is employed as the first-line treatment and involves the resection of the primary tumor along with any affected lymph nodes. This is followed by radiation therapy or radiotherapy + chemotherapy based on the presence of any adverse prognostic features. 3) Chemotherapy + radiotherapy or radiotherapy alone can be employed as the primary treatment. Surgery may be employed to remove any remnant cancer tissue.
Stage IVB
For Stage IVB cancer, radiotherapy along with chemotherapy or targeted therapy is usually employed as the first-line treatment. Surgery may be employed if the tumor shrinks sufficiently that it can be removed with surgery. Radiation therapy may be employed as palliative treatment.
Stage IVC
For Stage IVC cancer, chemotherapy, immunotherapy or targeted therapy are the treatment options. Radiation therapy may be employed as palliative treatment. 
Read about Staging and Treatment of Throat Cancer.
