Stage 4 breast cancer: complete remission with letrozole and palbociclib

What happened, in summary

A woman in her 40s presented in 2013 with worsening neck pain and shortness of breath when lying on her left side. CT showed left pleural effusion with partial lower-left-lobe collapse, a small right-middle-lobe nodule, multiple right-breast masses, pectoralis involvement, and axillary lymphadenopathy. Breast biopsy showed invasive ductal carcinoma with adenoid cystic features. The tumor was ER 62.5%, PR 62.5%, HER2 0%, and Ki-67 50%, consistent with hormone receptor-positive, HER2-negative breast cancer. She started ovarian suppression with goserelin, then tamoxifen 1 month later. The breast mass and axillary nodes shrank, while side effects included hot flashes, vaginal pruritus, and decreased libido. She underwent oophorectomy the next year. Disease was stable in 2015, but 6 months later tumor markers rose and exam findings worsened, so letrozole and palbociclib were added. By 2018, she had complete clinical remission after 3 years without recurrent breast disease. In 2021, while still taking letrozole and palbociclib, she developed fatigue, rash, headache, insomnia, severe cytopenias, and leukocytosis. Bone marrow biopsy showed 90% blasts; flow cytometry supported B-cell acute lymphoblastic leukemia, later classified as Philadelphia-positive. From 2021 to 2023 she received 4 cycles of hyperCVAD plus dasatinib. After a CNS-positive blast crisis, she started blinatumomab plus ponatinib. After cycle 1, bone marrow showed complete response with no molecular residual disease. Breast cancer remained in remission on letrozole, and monthly outpatient monitoring continued. Palbociclib was held when cytopenias appeared, but repeat blood counts worsened, leading to inpatient evaluation and urgent bone marrow biopsy before the leukemia diagnosis.