How do you approach adjuvant chemotherapy in early stage ER+ breast cancer who developed pneumonitis on ddAC?

Neulasta with ddAC can cause an interstitial pneumonia or reaction like pneumonitis. If she was node positive, younger and you think rechallenging her is reasonable (the pneumonitis was grade 1-2 and resolved quickly on steroids) then you could try to do the remaining AC q3wk without Neulasta to see if it recurs. If she didn't get Neulasta, don't want to rechallenge, or she doesn't need the AC then you can try weekly taxolx12 or TCx4 then endocrine therapy.

Generally agree. Would consider re-challenge with AC without neulasta only if the pneumonitis was mild and resolved. If more moderate to severe, would move on to weekly paclitaxel.

I would have to be convinced that the potential benefit of administering an anthracycline over alternatives like TC was large enough to justify the risk - such as triple negative with positive nodes or ER+/HER2- with at least 4 positive nodes. In that case, one option to consider would be sequential single agent chemotherapy, such as A followed by T followed by C as in CALGB 9741 (which had equivalent outcomes to AC followed by T); even if you still want to administer treatment every 2 weeks (especially for triple negative disease), you would likely need the pegfilgrastim only for the doxorubicin and this approach may help you to identify the agent responsible for the pneumonitis.

Agree with the team.

Considering the patient’s age and presence of high risk features, TC is an option as well as a 3 week cycle. CBC should be carefully monitored given the risks of febrile neutropenia.