The purpose of this study is to investigate if ultrasound can be helpful in the diagnostic work-up of oral tongue and floor of the mouth cancer. One important factor is how deeply the tumour invades the tissue, the so called depth of invasion (DOI). The investigator will measure DOI with ultrasound and compare the result with the same measurement by magnetic resonance imaging and the microscopic result after the surgery (PAD).

Ultrasound will also be used during surgery of the tumour to investigate if it is useful to better decide the depth of the tumour and thereby improving the operation.

The first part of this study will try to answer if ultrasound can improve the preoperative measurement of depth of invasion in tongue cancer and floor of the mouth cancer. The study population is new patients meeting the eligibility criteria presented to the hospital for treatment. Participants will be enrolled only after accepting the oral and written information and signing the written consent paper.

The examiner, one of three otorhinolaryngologists experienced in ultrasound, should be masked to the results of MRI. The first measurement is depth of invasion as well as thickness of the tumour in mm by palpation on awake patient. Thereafter the same measurements by ultrasound (BK Medical Medical flex focus 500, 18Mhz) with gel and protective cover is made with 0,5mm accuracy. Anesthetic gel or lingual block with carbocaine/adrenaline are provided as needed.

At the time of surgery the measurements above are done again on the patient in narcosis before the resection.

Images of the ultrasound measurements are saved for documentation. The results are compared to the corresponding measurements on MRI and also on PAD from the surgical specimen. PAD is considered gold standard.

Power calculation with help of biostatistician yielded a sample size of 55 patients, using a paired test with a 0,050 one-sided significance level will have 80% power to reject the null hypothesis that the proportions are not equivalent.

Analysis if ultrasound correctly classify the tumour´s DOI according to the TNM-classification 8th edition (<5mm, >5mm<10mm, >10mm) will be made.

The second part of the study will investigate if ultrasound during the surgical procedure can improve the discrimination of the deep margin of the tumour and thereby increasing the chance better surgical margins. The mucosal margins are marked in the usual fashion and the resection begins. After one fourth of the resection has been made, ultrasound is used to check that the deep margin is at least 10mm. This is repeated after one half and three quarters of the resection. At the end of the surgery a final ultrasound examination is made on the surgical specimen.

The margins obtained on PAD from resections done with ultrasound are compared to a matched retrospective group where the surgery was done without ultrasound.

After inclusion started our group started cooperation with another biostatician whom judged the analysis better be done from the quantitative variable of DOI in millimeter. This meant the power analysis shifted and a study population of between 15-23 participants was considered sufficient. Since the original plan was 55 participants we kept that number but after an interim analysis in may 2021 a total of 42 participants is now what we consider relevant in the study of DOI.

In our second endpoint studying ultrasound and surgical margin the interim analysis concluded that collection of patients for 2 years (may 2019 until may 2021) will be compared to a historical control group 4 years back in time (may 2015 until may 2019) and therefore the inclusion of that data stopped in may 2019.

Inclusion Criteria:

biopsy verified tongue cancer or floor of the mouth cancer. International Statistical Classification of Diseases and Related Health Problems (ICD) 10 C02.0-2 or C04.0-1

Exclusion Criteria:

• former surgery in the oral cavity
• former radiation to the oral cavity
• floor of the mouth cancer not available to ultrasound investigation
• floor of the mouth cancer extending to the gingiva
• patients not suitable for surgery
• T4 tumours according to TNM 8
• age under 18
• patients declining to participate

The data of measurements will be shared.

6 months after publication.

Coded, computerized IPD will be available upon a request with the serious intention to improve the scientific knowledge and transparency.

The ultrasound examiner should not be aware of the results of the MRI.