Can the CanRisk Tool be used to estimate breast cancer risks for both breasts after a patient has developed a first breast cancer? 

No. If a patient has developed a first breast cancer, the CanRisk Tool will only estimate the risk of contralateral breast cancer i.e. the risk of developing cancer in the unaffected breast (see https://canrisk.atlassian.net/wiki/x/AQAnFw).

We do not have any data on ipsilateral breast cancer risk at the moment. However, this is something that we are hoping to investigate in the future.