How Is the Actual Size of My Breast Tumor Determined?

Why a Physical Breast Exam Isn't Enough to Determine Tumor Size

How the Size of Your Breast Tumor is Determined

Several types of breast imaging can be used to try to locate and measure a breast mass. Mammograms, ultrasounds, and breast MRIs all have their advantages and disadvantages, with varying degrees of accuracy. Since tumor size is an important part of staging breast cancer, and affects your treatment decisions, you need to know the actual size of your tumor.

Why Your Best Guess at Tumor Size Isn't Accurate

A breast self-exam is one way of finding a lump, but you can only guess at its size. A clinical breast exam can confirm the presence of a lump and help document its location and perhaps estimate its size. A core needle biopsy takes a very small cross-sectional sample of the tumor, and may give additional clues to the overall size of the mass. Any information from these exams must be combined with imaging results.

Getting a Good Image of Your Breast Tumor

In the early process of getting all the details about your cancer, you get an increasingly clear picture of the tumor. When it comes to measuring the size of your tumor before surgery, doctors rely on the results of imaging studies. Let's compare the standard breast imaging methods:

  • Mammogram: Traditional film mammography can be used to image breast tissue, but is less accurate on dense breast tissue. If you are pre-menopausal, or have never been pregnant, your breasts my be dense enough to hide masses, making them harder to measure. But if you are post-menopausal, have fatty breast tissue, or have been pregnant, film mammography may accurately measure your tumor. Digital mammography works very well on dense breast tissue, and may be used to get a good measurement of a mass.
  • Breast Ultrasound: Without using compression, ultrasound is great for distinguishing between a fluid-filled cyst and a dense mass such as a tumor. Ultrasound can be used to make a measurement of a breast tumor. But it may be slightly less accurate than a mammogram, as it has been found to underestimate tumor size.
  • Breast MRI: MRI is noninvasive and painless, and uses no radiation to create a series of images of your breast tissue. While a mammogram may find your lump, an MRI might be needed to measure it if your breast tissue is dense or if your biopsy shows that the mass is larger than expected. MRI can also be used during neoadjuvant chemotherapy to monitor the progress of treatment. While MRI can create a clear image of your tumor, it tends to over-estimate the actual size in three dimensions.

Most Accurate Measurement: Surgical Pathological Results

Biopsies and imaging studies give a close ballpark measurement of your tumor. But you need the actual tumor size in order to make the best treatment decisions. Your surgeon will use the information from previous tests as guidance when removing your tumor. After a lumpectomy or mastectomy, your excised breast tissue will be combined with your biopsy tissue, and a pathologist will examine the actual mass. The pathological measurement of your tumor is the gold standard for tumor size. Your post-surgical pathology report will summarize your comprehensive diagnosis of breast cancer.

Reasons For Conservative Breast Cancer Surgery

Now that you know that your post-surgery pathology report is the best way to find out your tumor size, you may be asking, "So why don't we just do the surgery first and skip all these other tests?" Your biopsy and imaging studies are done in order to guide you and your surgeon in making the most conservative choice for breast surgery.

If a lumpectomy will remove your cancer, you may be able to avoid a mastectomy. But if neoadjuvant chemo may shrink your tumor before surgery, then you may need less tissue removed. In some cases, such as widely-scattered invasive breast cancer, a mastectomy might be the only surgical option. Having the most information and understanding the implications of your tests helps you make informed, intelligent treatment decisions.


Prediction of breast tumor size by mammography and sonography - A breast screen experience. Dummin L.J., Cox M., Plant L. (2007) Breast, 16 (1), pp. 38-46.

Prediction of breast cancer size by ultrasound, mammography and core biopsy. Golshan M., Fung B.B., Wiley E., Wolfman J., Rademaker A., Morrow M. (2004) Breast, 13 (4), pp. 265-271.

Breast cancer tumor size in MRI versus surgical pathological specimen: A correlative study. A. K. Swayampakula, A. Schwartzman, A. Saad, C. Dillis, J. Schreiman, G. Hobbs, J. Abraham. J Clin Oncol 26: 2008 (May 20 suppl; abstr 11550).

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