▁similar ▁to ▁those ▁of ▁other ▁cancer ▁cells . ▁ ▁A po pt otic ▁C TC s ▁are ▁traditional ▁C TC s ▁that ▁are ▁under going ▁apo pt osis ▁( program med ▁cell ▁death ). ▁These ▁may ▁be ▁used ▁to ▁monitor ▁treatment ▁response , ▁as ▁done ▁experiment ally ▁by ▁the ▁Ep ic ▁Sciences ▁method , ▁which ▁ident ifies ▁nuclear ▁fragment ation ▁or ▁cy top las mic ▁ble bb ing ▁associated ▁with ▁apo pt osis . ▁Me as uring ▁the ▁ratio ▁of ▁traditional ▁C TC ▁to ▁apo pt otic ▁C TC s — from ▁bas eline ▁to ▁ther apy — prov ides ▁cl ues ▁to ▁treatment ▁effic acy ▁in ▁target ing ▁and ▁killing ▁cancer ▁cells . ▁ ▁Small ▁C TC s ▁are ▁cy to ker atin - pos itive ▁and ▁CD 4 5 - negative , ▁but ▁with ▁sizes ▁and ▁shapes ▁similar ▁to ▁white ▁blood ▁cells . ▁Import antly , ▁small ▁C TC s ▁have ▁cancer - specific ▁bi om ark ers ▁that ▁identify ▁them ▁as ▁C TC s . ▁Small ▁C TC s ▁have ▁been ▁imp licated ▁in ▁progress ive ▁disease ▁and ▁different iation ▁into ▁small ▁cell ▁car cin omas , ▁which ▁often ▁require ▁a ▁different ▁th era pe ut ic ▁course . ▁ ▁C TC ▁clusters ▁C TC ▁clusters ▁are ▁two ▁or ▁more ▁individual ▁C TC s ▁bound ▁together . ▁The ▁C TC ▁cluster ▁may ▁contain ▁traditional , ▁small ▁or ▁C K - ▁C TC s . ▁These ▁clusters ▁have ▁cancer - specific ▁bi om ark ers ▁that ▁identify ▁them ▁as ▁C TC