SERPINB9 and neoplasm: As this apoptosis-propagating enzyme threatens cell survival, its presence is often accompanied by the expression of proteinase inhibitor 9 (PI-9), which specifically inhibits the function of granzyme B. Indeed, at least 40 % of HROC113 as well as HROC285 T0 M2 tumor cells expressed this enzyme inhibitor (Fig. 3e).