ICD-10 Code C04.8 – Malignant neoplasm of overlapping sites of floor of mouth (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C04.8 – Malignant neoplasm of overlapping sites of floor of mouth
What it is
This code identifies a malignant tumor of the floor of the mouth that spans overlapping subsites, so the exact point of origin cannot be assigned to a single category. Use it when documentation clearly states overlapping involvement.
Clinical signs
Findings may include a persistent oral mass, ulceration, pain, bleeding, or difficulty with speech and swallowing. Clinical features vary; refer to documentation and pathology when available.
When to use this code
Use C04.8 when the provider documents cancer involving overlapping sites of the floor of the mouth, such as extension across adjacent portions of that region. It is appropriate when the record does not support a more specific floor-of-mouth subsite. Confirm the diagnosis with the oncology, surgical, or pathology note.
Do not use for
Do not use this code for benign oral lesions, dysplasia, or cancers clearly arising in a single, non-overlapping floor-of-mouth site. Check documentation if the primary site is described elsewhere.
Coding tip
Code the most specific oral cavity site documented, and use C04.8 only when the lesion truly overlaps multiple floor-of-mouth sites.