How would you approach a patient with HR+, HER2- metastatic breast cancer who is endocrine resistant, with bone marrow involvement and pancytopenia?

Symptomatic bone marrow involvement (bone marrow carcinomatosis) is extremely rare in metastatic breast cancer and carries very poor prognosis. It is often associated with microangiopathic hemolytic anemia and DIC. Anemia is the most common manifestation and WBC and platelet counts are often not that affected. These patients almost always have diffuse skeletal mets.

I would recommend cytotoxic chemotherapy with transfusion support in such cases. There are several case reports and case series depicting the successful use of a variety of chemotherapeutic agents like paclitaxel, eribulin, anthracycline, and capecitabine, leading to recovery of blood counts and improved outcome.

Reference:

Kopp HG, Krauss K, Fehm T, et al. Symptomatic bone marrow ...

Bone marrow invasion in breast cancer is not uncommon, but it is typically focal in distribution and does not affect the blood counts, unless it becomes diffuse. Once there is diffuse spread, patients develop increasing degrees of anemia and thrombocytopenia, and less often some degree of neutropenia.

This topic is well described in the literature. Such patients require therapy with combination chemotherapy which shows definite activity. In the first cycle of chemotherapy, blood component support is often needed, but the blood counts typically start to show recovery after 2 cycles of chemotherapy. The disease can be controlled in 50-60% of the patients. This is based on my personal experience with more than half a dozen patients with metast...

Assuming this patient has progressed through AI+CDK4/6, SERD+CDK4/6 and there is no evidence of PI3KCA mutation or BRCA mutation on NGS, I would recommend capecitabine given the ease of administration/monitoring and transfusion support PRN. I would consider EPO, and would recommend IV Iron if the patient shows evidence of Iron restricted Anemia - low Fe with low/normal ferritin. Unfortunately TPO is not approved in this setting. If one expects prolonged neutropenia, I would consider AFC prophylaxis. We are pretty much treating like a leuk. Single agent abemaciclib is an option for patients in similar situations who have seen chemotherapy.

If the degree of bone marrow involvement is mild to moderate resulting in mild to moderate pancytopenia, I have seen very good results with various CDK4/6 agents. Otherwise, single agent chemotherapy is recommended. I usually start with weekly taxol with reduced dose sometimes.

Definitely a challenging clinical situation. I agree that cytotoxic chemotherapy should be administered based on the smaller studies mentioned by@Dr. First Last.

Due to ease of oral administration of capecitabine (although with a different side effect profile) and not being myelosuppressive, that would be an attractive option for ER+ Her-2- disease. Even eribulin is a reasonable option in 2nd line.

The question here needs to be corrected to Her-2+ since the patient received TCHP in the past. In that case, there are a number of options now: T-DM1, which has been there for the last 6-7 years based in EMILIA and TH3RESA studies. Now we have FDA approval for trastuzumab deruxtecan after progression on T-DM1 (Destiny Breast-01). Most recently, T...