In subgroup analysis, we found that patients with ER cancer, with metastasis, higher ASA score or TNM grade, confirmed diagnosis of breast cancer, multiple thyroid tumors, HER2+ or triple-negative breast cancer (TNBC) genotype, and recipients of active anticancer treatment (particularly chemotherapy) had extremely lower anti-RBD-IgG titers (Figures 2–7; Supplementary Figures 2, 5). This evidence concerns the gene ERBB2 and breast cancer.