Concurrent use of fam-trastuzumab-deruxtecan-nxki and larotrectinib in metastatic breast cancer: A case report

Abstract

A 60-year-old female presented in 2010 with left breast invasive lobular carcinoma, estrogen receptor (ER)+ (98%), progesterone receptor (PR)+ (98%), Her2 (2+), Ki67 (8%), Stage IIIC, T2 N3. She had lumpectomy, adjuvant chemo and radiation, took anastrozole until July 2019 when she had metastasis to bone. She started on palbociclib and fulvestrant. Imaging showed minimal improvement. In March 2022, her bone pain worsened and blood counts dropped and became transfusion dependent, bone marrow biopsy showed breast cancer metastases, ER+ (35%), PR−, Her2 (2+). PDL1 was negative, NTRK 1 was positive. She started on larotrectinib for her NTRK1 mutation, which showed some improvement and added fam-trastuzumab-deruxtecan-nxki for her Her2neu weekly positive, resulting in normalization of her blood counts. She has been on this combination which has never been reported, for over a year and has remained in remission with no significant toxicity. Targeting these two mutations simultaneously with possible additive effect can open some new trial ideas.