[6] He completed a fellowship in Medical Oncology at Memorial Sloan-Kettering Cancer Center in New York, and subsequently stayed on as a faculty member of its Breast Medicine Service.

During his time there, the institute emerged as a leading center of cancer research, therapies, and early stage clinical trials.

[5] Returning to the United States, he served at the Massachusetts General Hospital as the chief of its hematology and oncology divisions between 2010 and 2013.

[5] He was appointed physician-in-chief at Memorial Sloan Kettering Cancer Center in 2012,[7] and a professor of medicine at Weill Cornell Medical College in 2013.

[5] He resigned from Memorial Sloan Kettering Cancer Center in September 2018, after an exposé by The New York Times and the non-profit investigative journalism organization ProPublica, which called out that he had failed to report payments to the tune of millions of dollars from healthcare and drug companies in publications including The New England Journal of Medicine and The Lancet.

[13] Baselga also resigned from the boards of the drug company Bristol Myers Squibb and the radiation equipment firm Varian Medical Systems.

[15] In January 2019, AstraZeneca announced that they had hired Baselga as head of research and development in oncology, where he worked until his death.