▁monitor ▁the ▁disease ▁pro gression ▁over ▁time ▁could ▁facil itate ▁appropriate ▁modification ▁to ▁a ▁patient ' s ▁ther apy , ▁potentially ▁impro ving ▁their ▁pro gn osis ▁and ▁quality ▁of ▁life . ▁The ▁important ▁aspect ▁of ▁the ▁ability ▁to ▁pro gn ose ▁the ▁future ▁pro gression ▁of ▁the ▁disease ▁is ▁elim ination ▁( at ▁least ▁tempor arily ) ▁of ▁the ▁need ▁for ▁a ▁surg ery ▁when ▁the ▁repeated ▁C TC ▁counts ▁are ▁low ▁and ▁not ▁increasing ; ▁the ▁obvious ▁benefits ▁of ▁avoid ing ▁the ▁surg ery ▁include ▁avoid ing ▁the ▁risk ▁related ▁to ▁the ▁inn ate ▁tum or - gen icity ▁of ▁cancer ▁sur ger ies . ▁To ▁this ▁end , ▁techn ologies ▁with ▁the ▁requ is ite ▁sens itivity ▁and ▁reprodu ci b ility ▁to ▁detect ▁C TC s ▁in ▁patients ▁with ▁met ast atic ▁disease ▁have ▁recently ▁been ▁developed . ▁On ▁the ▁other ▁hand , ▁C TC s ▁are ▁very ▁rare , ▁often ▁present ▁as ▁only ▁a ▁few ▁cells ▁per ▁mill il iter ▁of ▁blood , ▁which ▁makes ▁their ▁detection ▁rather ▁challeng ing . ▁In ▁addition , ▁they ▁often ▁express ▁a ▁variety ▁of ▁markers ▁which ▁vary ▁from ▁patient ▁to ▁patient , ▁which ▁makes ▁it ▁difficult ▁to ▁develop ▁techniques ▁with ▁high ▁sens itivity ▁and ▁specific ity . ▁ ▁Types ▁C TC s ▁that ▁origin ate ▁from ▁car cin omas ▁( can cers ▁of ▁ep ith el ial ▁origin , ▁which ▁are ▁the ▁most ▁pre val ent ) ▁can ▁be ▁class ified ▁according ▁to ▁the ▁expression ▁of ▁ep ith el ial ▁markers ,