A mammogram is a low-dose X-ray examination of the breast used to detect changes that may indicate cancer. This imaging procedure is the primary tool for breast cancer screening and early detection. When an abnormality is identified, a more focused investigation is necessary. This targeted examination, called a diagnostic mammogram, thoroughly evaluates the area of concern to determine if the finding is harmless or requires further action.
Distinguishing Diagnostic from Screening Mammograms
A screening mammogram is a routine preventative procedure performed on patients who have no symptoms or signs of a breast problem. Its purpose is to detect early, non-palpable cancers in asymptomatic individuals. If a suspicious area is noted on a screening image, the patient is recalled for a diagnostic mammogram.
The diagnostic procedure is specifically tailored to the area of concern, whether it is a finding from a prior screening exam, a new lump, nipple discharge, or persistent pain. Unlike the standard two views taken during screening, a diagnostic mammogram often includes specialized, targeted views and magnification techniques. This focused imaging is frequently supplemented with a breast ultrasound, which uses sound waves to determine if a mass is solid or fluid-filled, providing a more detailed assessment of the abnormality.
The Statistical Likelihood of Cancer
The percentage of diagnostic mammograms that result in a cancer diagnosis is described by the Positive Predictive Value (PPV). For all diagnostic mammograms, the chance of finding cancer is low, typically falling in the range of 10% to 20%. This means that for every ten women who undergo a diagnostic workup, eight or nine will not have breast cancer.
The likelihood of cancer is not a fixed number and is influenced by the reason for the diagnostic exam. For instance, the probability is higher when the initial indication is a palpable mass compared to an abnormality found only on a prior image. The patient’s age also affects this statistic, as the incidence of breast cancer increases in older populations, leading to a higher PPV in women over the age of 50. When a diagnostic exam leads to a recommendation for biopsy, the PPV is higher, often ranging from 15% to 30%.
Common Reasons for Diagnostic Imaging That Are Not Cancer
The vast majority of diagnostic mammograms confirm that the area of concern is benign. One of the most frequent reasons for callback is the presence of cysts, which are fluid-filled sacs that can feel like a solid mass. Ultrasound is effective in identifying these structures and confirming they are simple cysts that do not require intervention.
Another common benign finding is a fibroadenoma, a solid tumor composed of glandular and fibrous tissue. These are common in younger women and often have smooth, well-defined margins on imaging. Calcifications, which appear as tiny white spots on the mammogram, are also a frequent finding. While certain patterns of microcalcifications can be suspicious, most calcifications are benign and may be related to aging, prior injury, or fibroadenomas.
Dense breast tissue can also necessitate a diagnostic workup, as it can obscure small cancers. Other benign conditions requiring evaluation include fat necrosis, which can mimic a mass after trauma or surgery, and duct ectasia, a condition involving the milk ducts. The diagnostic exam ensures that all ambiguous findings are thoroughly investigated.
Understanding Follow-up and Next Steps
The results of a diagnostic mammogram are communicated using the Breast Imaging Reporting and Data System, known as BI-RADS. This standardized system assigns a category from 0 to 6 to the findings, guiding the next steps for patient management. The category assigned reflects the radiologist’s assessment of the probability of cancer.
A BI-RADS 1 indicates a negative result, meaning the breasts are normal, while a BI-RADS 2 means a benign finding was identified. Both recommend a return to routine annual screening. A BI-RADS 3 finding is considered probably benign (less than 2% chance of cancer), and typically recommends a short-term follow-up in six months.
If the finding is more suspicious, it will fall into a BI-RADS 4 or 5 category, which recommends a biopsy to obtain a definitive diagnosis. A category 4 finding has a probability of malignancy between 2% and 95%, while a category 5 is highly suggestive of cancer, with a greater than 95% likelihood. The biopsy is a minimally invasive procedure that removes a small tissue sample for laboratory analysis, serving as the only way to confirm the presence or absence of cancer.