Clinicopathological Analysis of Breast Cancer-Related Paraneoplastic Syndrome: A Case Series of 6 Patients

Background: Breast cancer‑related paraneoplastic neurological syndrome (PNS) is rare, with an estimated incidence of approximately 0.3%. Neurological symptoms often precede the diagnosis of breast cancer; however, the clinicopathological characteristics, antibody profiles, and treatment outcomes remain incompletely defined, particularly in Asian populations. This case series from a large Chinese tertiary center aims to describe these features and highlight diagnostic challenges.

Case Description: Case Description: Six female with histopathologically confirmed invasive ductal carcinoma (median age 63 years, range 53–68 years) were included. Neurological symptoms preceded breast cancer diagnosis in 4/6 patients (mean interval 3–4 months) and occurred after prior breast cancer surgery in 2/6 patients (intervals of 4 and 5 years). Phenotypes included paraneoplastic cerebellar degeneration (2/6), brainstem encephalitis (1/6), limbic Encephalitis (1/6) and mixed sensorimotor/extrapyramidal syndrome (2/6). Antibody testing revealed anti‑Yo positivity in 3/6 patients, anti‑Ri positivity in 2/6, and one patient had combined anti‑Ri, amphiphysin, and PNMA2 antibodies; one patient tested negative. All patients underwent R0 resection and received systemic oncologic therapy. After a median follow‑up of 44 months, neurological outcomes were partial remission (2/6), stable disease (2/6), and progressive disease (2/6). The 5‑year overall survival rate was 83.3% (one non‑cancer death).

Conclusions: Neurological symptoms in patients with breast cancer‑related PNS frequently precede the cancer diagnosis. Anti-Yo and anti-Ri antibodies were the most detected types in this study. R0 resection combined with systemic therapy was associated with stabilization or improvement of neurological symptoms in some patients.