Abstract PO5-20-06: Paraneoplastic cerebellar degeneration in anti-Yo antibody and HER2-positive metastatic breast carcinoma
Authors: Kim You , Coogan Alison , Madrigrano Andrea 
Published: May 2024

Abstract
Paraneoplastic cerebellar degeneration (PCD) in the context of breast carcinoma affects less than 1% of patients. In most cases, breast cancer diagnosis follows several months or even years after the onset of neurological symptoms. The first association between PCD and occult gynecologic cancers (breast or ovarian) was identified in 1938 with the discovery of antibodies directed against cytoplasmic antigens of Purkinje cells (“anti-Yo antibodies”). Since then, evidence has grown significantly to support anti-Yo antibodies as excellent diagnostic markers of PCD with underlying gynecologic and breast carcinoma.
This case study evaluates a 57-year-old female who initially presented with headache and subacute cerebellar ataxia. Her symptoms progressed over a period of three months with multiple falls, onset of speech difficulties, and diplopia. She also reported 30-pound weight loss, which she attributed to dieting and starting semaglutide. Magnetic resonance imaging (MRI) of the brain and spine were unremarkable and autoimmune workup was normal. Cerebral spinal fluid (CSF) and serum studies demonstrated positive anti-Yo antibodies. Computed tomography (CT) of the abdomen and pelvis showed an enlarged left axillary lymph node concerning for metastatic disease with a 1.2cm focus of asymmetric density in the central inferior left breast parenchyma. Diagnostic mammogram one year prior was reportedly normal. Ataxia symptoms improved after a course of empiric intravenous immunoglobulins and steroids.
Ultrasound-guided biopsy of the left axillary lymph node revealed metastatic mammary carcinoma: estrogen and progesterone receptor negative and human epidermal growth factor receptor 2 (HER2)-positive, cT0N2aM0, ypTxN1aM0, stage IIIa (AJCC 8th edition). She underwent further metastatic workup, including repeat CSF studies and MRI. MRI of the spine was remarkable for multiple hemangiomas throughout the cervical, thoracic, and lumbar spine, with subsequent unremarkable bone scan. MRI of the abdomen was remarkable for right hepatic lobe hemangioma and a right adrenal nodule. CSF studies showed no sign of metastases. After multidisciplinary discussion, TCHP (docetaxel, carboplatin, trastuzumab, and pertuzumab) neoadjuvant therapy was initiated and repeat imaging demonstrated favorable treatment response with a shrinking axillary mass; no primary breast mass was identified. The patient underwent left sentinel lymph node biopsy with a positive frozen section intraoperative for invasive cancer, therefore proceeded with left axillary lymph node dissection. She was offered a mastectomy but elected for only axillary surgery. Pathology revealed 1 of 14 lymph nodes were positive for metastatic ductal carcinoma. She remains in a rehabilitation center and her ataxia is improving, but her functional status remains below baseline. She is undergoing radiation to whole breast and regional lymph nodes.
With this case, we aim to continue to build upon the limited base of the exceedingly rare presentation of breast cancer-associated paraneoplastic syndrome. In addition, several studies and case reports have demonstrated a strong correlation between HER2 overexpression and anti-Yo associated PCD. As we continue to diagnose and monitor breast cancer patients, we could consider starting to screen for anti-Yo antibodies in HER2-positive patients to gain insight into a patient’s prognosis and development of PCD.
Citation Format: You Kim, Alison Coogan, Andrea Madrigrano. Paraneoplastic cerebellar degeneration in anti-Yo antibody and HER2-positive metastatic breast carcinoma [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-20-06.