This unexpected discovery in bilateral breast cancer

This unexpected discovery in bilateral breast cancer

French researchers have made a major discovery about bilateral breast cancer, a cancer which is characterized by the presence of tumors in both breasts, which would improve the care of affected women.

Great progress on the bilateral breast cancera cancer characterized by the occurrence of a tumor in each of the two breasts. For the first time, a study conducted by the Institut CurieInserm and the German Breast Cancer Group and published in the journal NatureMedicine on March 6, 2023 showed, thanks to very advanced sequencing technologies, that the two tumors were independent of each other and D’different origin. But also that the type of each tumor (the tumor can be of the luminal, HER2 or triple negative type) influenced the tumor microenvironment (the environment around the tumor cells, editor’s note) in the other breast, in particular on the immune system, and modified response to treatment. This great discovery could therefore make it possible to better adapt the treatment and to improve the care of women with this type of cancer.

What is bilateral breast cancer?

Breast cancer is considered bilateral when both breasts are affected by a malignant lesion (a tumour) either simultaneouslyeither in a period of less than 6 months, defines Inserm. This type of cancer concerns between 2 and 11% of all breast cancers, with an ever-increasing incidence.

Mammography of bilateral breast cancer ©

What causes these tumours?

The very small size of the patient group (a small cohort of 6 patients has been genomically analyzed) makes it impossible to finda gene common to all these tumors. “It’s a possibility we can’t rule out but we don’t see any element that goes in this direction. Bilateral tumors may not be rare, but their occurrence turns out to be independent and can be attributed to bad luck“, continues Joshua Waterfall.

“Their occurrence can be attributed to bad luck”

These bilateral tumors would therefore be genomically independent, in terms of mutations, copies of alterations and expression. But their occurrence could be influenced by microenvironmental factors in cells and tissues such as:

  • The surrounding blood vessels
  • immune cells
  • Fibroblasts
  • The other cells
  • Signaling molecules
  • The extracellular matrix.

Which treatment according to the tumour?

According to the results of this study, the response of the immune system and the response to neoadjuvant therapy (given to patients before surgery) would not be not the same depending on the nature of the tumors. Thus, researchers and doctors have discovered that:

► The immune system does not react in the same way if the right and left tumors are from different subgroups (luminal, triple negative or HER2).

► One luminal tumor (most common form of breast cancer: these are hormone-sensitive tumors that have estrogen and progesterone receptors) usually does not respond to neoadjuvant treatment

► In the presence of a triple negative tumor, the immune response and the response to treatment are increased. “A systemic mechanism, for which there is no explanation yet“, explains Joshua Waterfall, researcher at Inserm who conducted the study.

In view of these results, the researchers and doctors recommend considering these tumors as two different entities before deciding on a treatment which would target them both. “Since the two tumors are independent but can influence each other, the choice of treatment can be complex. We hope that our results can guide caregivers in their decisions and improve patient care.“, continues Dr. Joshua Waterfall.


– Bilateral breast cancer: the first complete study reveals that the tumors are independent of each other, press release, Inserm, March 6, 2022. This work relates to a cohort of 17,500 patients of all ages of which 404 were carriers of bilateral breast cancer (i.e. 2%) initially, then a small cohort of 6 patients was analyzed on the genomic level in a second step.


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