Finding a lump in your breast is scary! Fortunately, most lumps in the lactating breast (breasts that produce milk are called lactating breasts) are either milk-filled glands or an inflammation, such as a blocked duct or mastitis. If the lump is tender, it is probably mastitis. See our Mastitis article for information on treating this condition.

Some people, especially those with lighter skin tones, may notice a red coloring to their skin on the breast as a sign of worsening infection. If the lump does not go away after a week of careful treatment for a blocked duct/mastitis or if you are feeling generally unwell or have a warm or hot breast or high fever, please consult your doctor. A small percentage of cases of mastitis go on to develop a breast abscess that requires antibiotics and drainage.

A less common type of breast cancer, inflammatory breast cancer, does not present with a lump, but instead presents with swelling, tenderness, thickening, and redness covering more than 30% of the breast. It is most common in women under the age of 40. If treatment with antibiotics does not show a reduction in symptoms in 7 to 10 days, further tests such as ultrasound or scans and biopsy should be conducted. See Inflammatory Breast Cancer fact sheet.


Although breast cancers during lactation are extremely rare, they are known to occur. [1] Changes or abnormalities of any kind in your breast should be investigated with the same level of concern regardless of whether you are breastfeeding or not. Research shows that breastfeeding reduces the incidence (cases) of breast cancer. [2]

If you need a mammogram while you are breastfeeding, it can usually be performed on your lactating breasts. However, it is not necessarily the diagnostic method of choice for high risk (e.g. BRCA carriers) women under 30 [3] . Your healthcare professional will be able to talk through your options with you.
Contrary to advice sometimes given, it is possible to read a mammogram of a lactating breast. Due to milk production, tissue in a lactating breast is denser than in a non-lactating one. This may make it harder to read the results. If your health system allows, ask for a radiologist experienced in reading mammograms of lactating breasts.

The density of the tissue in your breast can also be influenced by the frequency and timing of your baby’s feeds. When possible, express milk or bring your baby and breastfeed immediately prior to the procedure to reduce the amount of milk in the breast before imaging. X-rays do not affect human milk [4], so you can safely resume nursing immediately after the mammogram.

If the lump you’ve discovered needs closer examination, you can feed immediately after fine-needle aspiration as well as after a biopsy or other surgery. It is important to let your doctor and/or surgeon know that you are breastfeeding so they can select appropriate medications for you.

In some countries and health systems, ultrasound is more commonly used for initial assessment and you can safely resume nursing immediately. If the lump appears suspicious, an MRI with a contrast medium to improve the clarity of the breast structure may be performed. The 2019 Academy of Breastfeeding Medicine clinical protocol on imaging and nuclear medicine during lactation states with respect to gadolinium, the most commonly used contrast medium for breast MRIs, “The taste of the breast milk may be altered slightly after intravenous gadolinium-based contrast, but it is not harmful to the breastfeeding child”. [5] If questions arise or if another contrast medium is to be used, you may ask the radiologist to consult LACTMED, the drugs and lactation database, or another reputable up-to-date source to ascertain safety while breastfeeding.

If you have a biopsy or surgery, you may need to adjust breastfeeding positions for a time to avoid putting pressure on the sore area, or to express milk while you heal. Your local LLL Leader can help with suggestions – find local support here.

See also, Cancer and Breastfeeding.

  1. Unar- Munguia, Breastfeeding Mode and Risk of Breast Cancer: A Dose–Response Meta-Analysis,Journal of Human Lactation, Vol 33, Issue 2, 2017;;
    Ying Zhou et al, Association Between Breastfeeding and Breast Cancer Risk: Evidence from a Meta-analysis, Breastfeeding Medicine. Apr 2015: 175-182;
  2. Lööf-Johanson Margaretha et al, Breastfeeding Associated with Reduced Mortality in Women with Breast Cancer, Breastfeeding Medicine, July 2016, 11(6): 321-327.
  3. Carmichael, H., Matsen, C., Freer, P. et al. Breast Cancer Res Treat (2017) 162: 225.
  4. Philip O. Anderson, New and Unusual LactMed Topics, Breastfeeding Medicine. Nov 2016, 11(9): 430-432 DOI: 10.1089/bfm.2016.0136
  5. Katrina B. Mitchell, Margaret M. Fleming, Philip O. Anderson, Jamie G. Giesbrandt, and the Academy of Breastfeeding Medicine, ABM Clinical Protocol #31: Radiology and Nuclear Medicine Studies in Lactating Women, Breastfeeding Medicine, 2019, 14

Updated May 2022 by Ann Calandro, MSN, RN, IBCLC, Dr. Nan Jolly, and Dr. Justice Reilly