Surgery to Oligometastatic Breast Cancer after Excellent Response to Palbociclib and Letrozole Therapy: Pitfall of Ultrasound Therapeutic Evaluation

A 48-year-old woman with regional recurrences of breast cancer in the axillar and supraclavicular regions was referred to our hospital. Under the diagnosis of recurrent luminal breast cancer with a high Ki-67 labeling index of >30% and a disease-free interval of 13 years, the patient began to receive palbociclib, letrozole, and luteinizing hormone-releasing hormone agonist, resulting in marked response of the supraclavicular lesion and stable disease of the axillar lesion on ultrasound (US) evaluation. Positron emission tomography (PET)/computed tomography of the axillar and supraclavicular foci showed high and no avidities before and after treatment, respectively. The unmovable neck lesion became movable with the treatment. The patient, therefore, underwent surgical resection of the 2 metastatic foci to examine the discordant therapeutic efficacy against the 2 metastatic foci on 2 image modalities, that is, US and PET, and to possibly get a cure of the breast cancer oligometastasis. Pathological examination showed marked fibrosis and scant cancer cell residuals with microcalcifications in the neck tumor and massive sarcoid-like reaction with scant cancer cell residuals in the axillary nodes. The residual cancer cells showed estrogen and progesterone receptor positivities, human epidermal growth factor receptor type 2 negativity, and an extremely low Ki-67 labeling index of 2.5%. The patient recovered uneventfully and has continued palbociclib-containing endocrine therapy for 1 year without any recurrences. Breast oncologists should well understand the basic principles of internal echo formation on US and take the presence of sarcoid-like reaction in the cancer cell clusters into consideration on the therapeutic evaluation of metastatic breast cancer.