A 35 years old woman was diagnosed with clinical stage 2, grade 3, hormone receptor positive, human epidermal growth factor receptor 2 (HER2) negative invasive ductal carcinoma, with ki-67 of 60%. She was treated with neoadjuvant chemotherapy with dose dense adriamycin and cyclophosphamide followed by paclitaxel. Six days following the third cycle of paclitaxel the patient presented with rapidly progressive weakness, proximal paresthesia and decreased sensation in both legs. Physical examination revealed hypoesthesia below level, proximal and distal weakness in both lower limbs and absence of reflexes. MRI of the spine demonstrated diffuse leptomeningeal enhancement from T11 to S1 including the cauda equina roots. The rapidly progressive neurological symptoms and the MRI findings were initially interpreted as leptomeningeal spread. High dose dexamethasone was promptly initiated and the patient was urgently planned for radiotherapy and received the first fraction of 3 Gy to level T11-S1. Further workup included lumbar puncture which showed elevated protein level (350 mg/dL), negative cytology for malignancy and EMG which demonstrated demyelinating injury compatible with Guillain-Barre syndrome (GBS). A diagnosis of GBS was made and treatment with intravenous immunoglobulins (IVIG) was initiated, followed by a gradual clinical improvement. Two months after the initial diagnosis, she had a near complete resolution of her neurological deficits. This case illustrates both the tendency to ascribe new symptoms and clinical findings in cancer patients to progressive disease, and the importance of keeping a wide differential diagnosis for non-cancer etiologies when treating our patients.