This discrepancy in the results might be due to different factors including ELISA kits with different performance, choosing criteria for normal individuals, number of chosen samples, the difference in CD44 isoforms present in serum, etc. Soluble CD44 found in 140 breast cancer patients ranged from 220.8 ng/mL to 1216.7 ng/mL while the median serum level was ≥ 417.4 ng/mL with different levels of the protein in different subtypes of breast cancer (406.4 ng/mL in luminal, 506.8 ng/mL in triple-negative and 462.5 ng/mL in HER2-enriched subtype)85. This evidence concerns the gene ERBB2 and breast cancer.