Blood nipple discharge with linear branching microcalcifications is indicative of?

The presence of blood nipple discharge accompanied by linear branching microcalcifications is most indicative of ductal carcinoma in situ (DCIS). DCIS is a non-invasive breast cancer that originates in the milk ducts and can present with various abnormalities on imaging studies, including mammography. One of the characteristic findings for DCIS is the appearance of linear branching calcifications, which are typically seen due to the calcification of the ducts as a result of malignancy.

The blood nipple discharge can occur due to the rupture of abnormal ductal structures or the presence of small tumors within the ducts. In contrast, while invasive ductal carcinoma can also present similarly, the specific combination of blood discharge and linear branching microcalcifications is more associated with DCIS, as it reflects a localized process that has not yet invaded the surrounding tissue.

Invasive lobular carcinoma and mucinous carcinoma typically do not present with this specific pattern of calcifications and discharge. Invasive lobular carcinoma is known for its subtle growth pattern and may not lead to the same types of calcifications. Mucinous carcinoma, on the other hand, often shows a different histological pattern and presentation on breast imaging. Thus, the characteristics described in the question align most closely with DCIS.