SIX1 and cancer: In agreement, immunohistochemistry analysis on breast phyllodes cancer showed that tumor grade was positively correlated with SIX1 protein level.[16] By activating proproliferative and prosurvival mechanisms, SIX family members promoted expansion of progenitor cell populations prior to differentiation.[52–54] In addition to breast cancer, higher SIX1 level was also linked to poor differentiation in gastric tumor[47] and prostate cancer.[55]