ICD-10 Code C50.31 – Malignant neoplasm of lower-inner quadrant of breast, female (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C50.31 – Malignant neoplasm of lower-inner quadrant of breast, female
What it is
C50.31 identifies a malignant tumor in the lower-inner quadrant of the female breast. Use it when documentation specifies that exact breast location and confirms cancer.
Clinical signs
Clinical features vary; refer to documentation. Standard findings may include a breast mass, skin or nipple changes, or imaging and biopsy results confirming malignancy in the lower-inner quadrant.
When to use this code
Use this code when the provider documents primary breast cancer in the lower-inner quadrant of the female breast. It is appropriate for confirmed malignancy, including cases based on pathology or clear clinical diagnosis. If the record only says “breast cancer” without laterality or quadrant, check documentation.
Do not use for
Do not use it for benign breast disease, carcinoma in situ, or unspecified breast location. If the tumor site is not documented as the lower-inner quadrant, choose the more accurate code.
Coding tip
Verify both the breast side and quadrant in the note before assigning C50.31.