 This research examined how the interaction between two types of breast cancer cells, one sensitive and one resistant to a certain type of drug, affects their ability to survive and thrive under treatment. It was found that the presence of the resistant cells helped the sensitive ones to survive and proliferate better, which could be explained by the fact that the resistant cells produced a hormone called estradiol, which stimulated the sensitive cells growth. This phenomenon was observed in both mono and co-cultures, but it was only effective in the latter. Additionally, mathematical models were used to predict the effects of this phenomenon on the overall outcome of the treatment. This article was authored by Reena Emmond, Jason I. Griffiths, Vince Cornel Gromas and others.