ICD-10 Code C04 – Malignant neoplasm of floor of mouth (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C04 – Malignant neoplasm of floor of mouth
What it is
C04 identifies a malignant tumor arising in the floor of the mouth, the area under the tongue. Use it when the documentation states cancer in this specific oral site.
Clinical signs
Findings may include a persistent oral mass, ulceration, pain, bleeding, or difficulty with speech and swallowing. Clinical features vary; refer to documentation.
When to use this code
Use C04 when the provider documents primary cancer of the floor of mouth, including a lesion confirmed as malignant in that location. You may also use it when pathology or specialist notes clearly identify this site. Check documentation if the record only says oral cancer without a precise subsite.
Do not use for
Do not use C04 for benign oral lesions, dysplasia, or cancers of other mouth sites such as the tongue or gum. If the primary site is unclear, check documentation.
Coding tip
Confirm the exact anatomic subsite in the operative, pathology, or oncology note before assigning C04.