ICD-10 Code C50.5 – Malignant neoplasm of lower-outer quadrant of breast (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C50.5 – Malignant neoplasm of lower-outer quadrant of breast
What it is
C50.5 identifies a malignant tumor located in the lower-outer quadrant of the breast. Use it when the record specifies this breast subsite and confirms cancer.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include a breast mass, skin or nipple changes, or imaging and biopsy results confirming malignancy in the lower-outer quadrant.
When to use this code
Use this code when the provider documents primary breast cancer in the lower-outer quadrant. It also applies when pathology, imaging, or operative notes clearly identify that breast subsite.
If the note only says breast cancer without location, check documentation before assigning C50.5. Code the documented site exactly, and do not infer a quadrant from limited evidence.
Do not use for
Do not use C50.5 for benign breast disease, unspecified breast malignancy, or cancer in another quadrant. Check documentation if the lesion is metastatic rather than primary breast cancer.
Coding tip
Code the exact breast quadrant only when the record supports it; otherwise, use the unspecified breast cancer code after reviewing documentation.