A 22-year-old female has a firm, non-tender breast mass. What is the most likely diagnosis?

The diagnosis of a firm, non-tender breast mass in a 22-year-old female is most consistent with a fibroadenoma. Fibroadenomas are the most common benign breast tumors in this age group and typically present as painless, mobile, firm masses. They often feel rubbery and can vary in size.

The histological findings include glandular and stromal components, which are characteristic of this type of benign lesion. While other breast conditions can present with lumps, their characteristics often differ significantly from those of fibroadenomas.

For instance, breast fat necrosis usually occurs after trauma or surgery and might present with tenderness or skin changes. Fibrocystic changes can cause lumpy or cystic breast tissue but are frequently associated with tenderness and fluctuate with the menstrual cycle. Intraductal papillomas may cause nipple discharge and are typically found in patients slightly older than this population. The specific characteristics of the firm, non-tender breast mass align closely with the expected presentation of a fibroadenoma, making it the most likely diagnosis in this scenario.