▁et ▁al . ▁have ▁drawn ▁attention ▁to ▁the ▁fact ▁that ▁T G F - β , ▁which ▁acts ▁in ▁the ▁ep ith el ial ▁cells ▁of ▁the ▁m amm ary ▁g land ▁as ▁a ▁pot ent ▁tum or ▁suppress or ▁at ▁the ▁early ▁stages ▁of ▁cancer , ▁can ▁affect ▁tum or ▁development ▁via ▁interaction ▁with ▁on c ogen ic ▁cy tok ines . ▁In cre ased ▁expression ▁of ▁T G F - β ▁has ▁been ▁associated ▁with ▁the ▁pro gression ▁of ▁tum or , ▁which ▁has ▁often ▁been ▁observed , ▁e . g ., ▁at ▁the ▁later ▁stages ▁of ▁breast ▁cancer . ▁The ▁role ▁of ▁T G F - β ▁in ▁ep ith el ial - st rom al ▁migration ▁during ▁tum or ▁pro gression ▁has ▁not ▁been ▁studied ▁sufficiently . ▁T G F - β ▁is ▁supposed ▁to ▁be ▁a ▁key ▁reg ulator ▁of ▁the ▁interactions ▁between ▁the ▁tum or ▁and ▁st rom a , ▁which ▁prom otes ▁collect ive ▁cell ▁migration ▁in ▁breast ▁cancer . <0x09> ▁ <0x09> ▁It ▁has ▁been ▁established ▁that ▁leader ▁cells ▁express ▁pod op lan in , ▁a ▁transm emb rane ▁g ly cop rote in ▁that ▁is ▁expressed ▁under ▁normal ▁conditions ▁in ▁kid ney ▁pod ocy tes , ▁type ▁ 1 ▁lung ▁al ve olar ▁cells , ▁ske let al ▁mus cle ▁cells , ▁pla cent a , ▁etc . ▁Pod op lan in ▁expression ▁in ▁breast ▁cancer ▁cells ▁indu ces ▁cell ▁migration ▁and ▁invasion ▁with ▁the ▁formation ▁of ▁fil op odia ▁and ▁simultane ous ▁ret