Everytime you go for a breast imaging examination (e.g. mammogram, breast ultrasound, breast MRI, etc.), the radiologist interpreting your study almost always assigns a BI-RADS Score to the exam.
BI-RADS (Breast Imaging-Reportinge And Data System) is a system designed by the American College of Radiology (ACR) to give the doctor who ordered your breast imaging exam a quick indication as to whether your exam is normal or abnormal.
There are 7 possible scores that can be given: 0, 1, 2, 3, 4, 5, and 6. Here is what they mean.
Category 0: there is an area on the examination which either needs further imaging/testing or needs to be compared to prior exams to determine if it is stable or something new
Category 1 and Category 2: there is no evidence of breast cancer on the exam
Category 3: there is an area on the examination which is most likely benign (non-cancerous) but should be followed with a repeat exam in a few months to make sure that the area is not changing; chance of breast cancer <2%
Category 4: there is an abnormality on the examination which may need biopsied to exclude breast cancer; chance of breast cancer 2-95% (a wide range!); because of the large range, some places further sub-divide this category into 4a, 4b, and 4c categories to give a more targeted likelihood of cancer
Category 5: there is an abnormality on the examination which needs biopsied to exclude breast cancer; chance of breast cancer >95% (therefore, a highly suspicious classification)
Category 6: breast cancer has already been diagnosed but has not yet been definitively treated
There are two important points to make.
First, different exams can have different codes. The same abnormality can look non-cancerous on one exam (thus, coded category 1 or 2) but look cancerous on a different exam (thus, coded category 4 or 5). Therefore, a category 1 or category 2 coding on your exam does NOT mean you don't have breast cancer...it simply means there is no evidence of breast cancer on that particular exam. When the same abnormality is seen on different exams, the information from all these exams is "put together" to better define the abnormality and devise a plan of action for it (e.g. biopsy, follow up, or even "no further action needed").
Second, when an abnormality is considered "probably benign" (category 3), there is still a chance the abnormality can be cancerous. That means when you have a follow up exam in 6 months, there may be a subtle change in the abnormality which then prompts a biopsy. The biopsy could be cancerous. However, in the overwhelming majority of these cases, there is no adverse affect on the prognosis (treatment outcome) by having waited because of the follow up exams. Having said that, when I think something is "probably benign," I usually like to give my patients the option for biopsy (or at least the option of evaluation of the abnormality with a different/more definitive imaging test) because there are some patients who are uncomfortable with the slight uncertainty associated with this follow-up option.