Treatment of Minimal Residual Disease in Breast Cancer: A Longitudinal Case Study

The presence of micrometastatic disease will ultimately determine the breast cancer-specific mortality of patients treated according to current guidelines. Minimal residual disease (i.e., occult tumor, not detected by conventional tests) may exist in two forms: a dormant form of only micrometastasis and a more aggressive "awakened" form where CTCs (circulating tumor cells) are actively disseminating. The hypothesis is that patients with CTCs have a more advanced or aggressive disease (that the cancer has "awoken" and there is active dissemination), whereas those patients with only micrometastasis have "dormant" disease and, although at risk of future relapse, may not do so for many years. This case study shows how determining the presence of both CTCs and bone marrow micrometastasis could be used to monitor disease activity and determine treatment changes before the appearance of metastatic disease. Presented is the case of a 53-year-old postmenopausal woman who presented with a T2N1M0 invasive ductal breast cancer. She had been treated with partial mastectomy, axillary dissection, local radiotherapy, and adjuvant chemotherapy. As the cancer was estrogen receptor-positive, she was taking tamoxifen. Two years into treatment, she was assessed for minimal residual disease and was found to be positive for CTCs and bone marrow micrometastasis. Her treatment was changed to letrozole and differing bisphosphonates. The minimal residual disease was finally eliminated, and at 16 years post-initial treatment, there was no evidence of relapse. The detection of minimal residual disease can be used to monitor treatment effect and change therapy in order to maintain the asymptomatic status of the patient and prevent disease progression.