While there are no large datasets available for breast cancer patients treated with oncolytic virotherapy, evaluation of CD19 mRNA expression in patients treated with FEC therapy indicated CD19 trended towards being a predictor of complete pathological response in a Her2(-) ER(-) restricted patient group [AUC = 0.657, ROC p value = 0.02, Mann–Whitney p value = 0.054], and was a predictor of pathological response across combined breast cancer patients treated with FEC [AUC = 0.729, ROC p value < 0.01, Mann–Whitney p value < 0.01]. The gene discussed is CD19; the disease is breast cancer.