What is your approach to adjuvant HER-2 directed therapy in a patient who developed cardiotoxicity following neoadjuvant TC-HP?

Depending on the risk of the cancer and how bad the cardiotoxicity was, it may be worth trying to reinstitute HER2-directed therapy. Typically I hold HER2-directed therapy for a month at a time (until the EF gets to 50% or higher at which point I reinstitute) and involve a cardiologist familiar with our drugs who can medically manage the cardiotoxicity proactively. 

While I agree with a number of the comments above, including omission of pertuzumab if cardio-oncology feels comfortable with rechallenging her with trastuzumab, my recommendations would be tempered by her stage at presentation and response to neoadjuvant therapy - if she had clinical stage II disease at presentation and achieved a pCR with her neoadjuvant therapy, her prognosis should be excellent, and there is no data that it will be improved by further HER2-targeted therapy. In the trials comparing 12 months to shorter durations of trastuzumab, there is very little (if any) absolute benefit for the longer course of treatment - if the patient has no contraindications I'm OK with giving 12 months of trastuzumab but not if there's a risk of doing permanent damage to her heart, especially given the rarity of cardiac complications with the anthracycline-free regimens      

In addition to the answers above, I would also consider re-challenging with trastuzumab only (without pertuzumab) since the APHINITY data showed only a very small absolute difference in DFS and there is no overall survival benefit demonstrated to date with pertuzumab in the adjuvant setting.

There is some data that beta blockers can help prevent some cardiac toxicity. I would wait until the EF was greater than 50%; make sure that any cardiovascular comorbidities are managed, and consider a low dose of carvedilol during therapy. However, the EF would need to be monitored after every cycle, and the patient should be followed by a cardiologist

Notably, most women on the pivotal adjuvant North American and HERA studies were able to successfully rechallenge with trastuzumab after a hold due to a "significant" LVEF change while receiving trastuzumab, so i am comfortable with the trastuzumab rechallenge strategy as was adopted on those studies  and in population based studies. However, as outlined by Drs. Hershman and Carey, cardio-oncology is a growing field and I enlist their input for patients being treated off-study and support their research efforts so that we can collectively understand the more nuanced issues around HER2-directed therapy mediated risk.

I agree with the recommendations above, omitting the pertuxumab and rechallenging with trastuzumab when EF recovers to >50%, optimizing cardiac care with beta blockers and/or ACE inhibitors. When rechallening with trastuzumab, one can consider weekly dosing at 2mg/kg at first, monitoring with echo regularly.