SPP1 and neoplasm: Human osteopontin is subject to alternative splicing, and the molecular size of this protein is known to be variable ranging between 41 and 75 kD.15 As illustrated in Figure 6, there was 10‐fold increase in the detection of the upper osteopontin protein band at around 65 kD in the P3 tumours compared with P1 and P2 subtypes.