Could doctors play down breast cancer until they get biopsy results or can they tell by scan?

Play down?: I don't know what you mean by that but the diagnosis of breast cancer is made under the microscope looking at tissue obtained from a biopsy or surgery. Mammos, scans, and even physical exam can sometimes give us a very good idea of whether there is cancer or not but we need tissue. Furthermore, different cancers will be treated differently so we have to know.

Pathology report: The only way to know if there is a breast cancer is to get a biopsy (piece of tissue). We can look at mammograms and have a "high suspicion" but the definitive answer will come in the biopsy report. When a core needle biopsy is done, the results are ready in 24-72 hours.

Cancer: Radiologists can assign a probability of malignancy based on imaging features, but can't tell for certain, so the biopsy is necessary for a definitive answer.