Using human milk to study breast cancer

Donating human milk is really useful for babies and parents who need it, but these donations are also now being used to help us advance science. Specifically, to learn more about breast cancer. Julia Ravey spoke to Alicia-Jane Twigger from the University of Cambridge is doing just that…

Alicia - What we found overall is that women who breastfeed and lactate actually have an overall low risk of breast cancer, but there are some factors that influence that. That could include how old a woman is when she becomes pregnant and lactates, as well as the duration of the breastfeeding experience.

Julia - These studies so far are all correlational. Do we have any ideas about if there could be a mechanism and what that could be?

Alicia - There are actually some animal studies that have looked into this and have found that there seems to be some remnant cells after parity called parity induced cells. There is some evidence to suggest that there are epigenetic changes that occur within the cells. Of course, this has been really difficult to validate in humans because getting human tissue, especially during pregnancy and lactation, is so difficult.

Julia - So how are you using human milk to help us better understand breast cancer risk?

Alicia - So, what we've done as part of our study, is we've centrifuged fresh milk samples, and then we're able to extract the cells, and we've done a whole bunch of different analyses, including growing the cells in culture, examining the protein profile and the transcriptomic or RNA profile, to then see how similar the cells and the breast milk are compared to the cells in the actual breast itself.

Julia - And what have you found in this research so far?

Alicia - So, what we found is that the cells in milk seem to predominantly be either the secretory cells in milk or the immune cell subtypes, and the secretory cells in milk have a very similar profile to luminal progenitor cells in the breast tissue.

Julia - And what do luminal progenitor cells normally do in breast tissue?

Alicia - Evidence from mass studies have found these luminal progenitor cells seem to be the ones that actually then differentiate into the milk secretory cells, but they also seem to be the cell of origin for many aggressive breast cancer subtypes.

Julia - So, if these are being excreted in the milk, drawing lactation, do you think that this could potentially be a mechanism whereby these cells are being reduced in their numbers and this might be some sort of mechanism that is linking breastfeeding and breast cancer?

Alicia - There's two schools of thought as to why cells enter the milk. One reason could be that they somehow have a benefit for the infant, the other might be, as you say, like a clearing mechanism of the metabolically active, almost damaged cells into the milk. And it's the supportive mechanism for mother to clear out these really energy exhausted cells.

Julia - With these studies, you found that, in human milk, there are these cells that look similar to what we have in the breast tissue, and these cells are potentially progenitors for cancerous cells down the line. What's the next step there? We found the cells, now what are we going to look for?

Alicia - Something that I'd like to do in the future is to look at how DNA damaged these cells are and whether there are mutations, and then see if we can use that as a proxy to then measure a women's potential for getting breast cancer. Obviously, the great thing about getting the cells out of the milk is it's not invasive, and we can do this across a really large population.

Julia - And if this was a potential screening mechanism, what would be the case for individuals who do not lactate?

Alicia - That's a good question. I think we would only be able to do this, as I said, in this timeframe for women who are pregnant and lactating, or post-pregnancy during lactation. But hopefully, overall, this will give us a better insight into what's happening in the breast during these changes, and whether there might be strategies to try and encourage damaged cells to either be cleared or for them to be reprogrammed somehow using therapeutic strategies.

Julia - How important has human milk donation been to your research?

Alicia - It's been hugely important, actually. I feel so lucky to be supported by a huge community of women who have donated milk. Historically, I found that women who are donating to breastfeeding research are so interested, they're so supportive, and obviously I couldn't do my work without them.

Julia - It's really interesting to see human milk be used in this way to advance science.

Alicia - Yeah, absolutely. Obviously, this is my passion; this is something that I have found fascinating for a very long time. I'm very grateful to the community for their support in providing samples. I'm really excited to be doing this.