No mitogen is necessary as they divide spontaneously. Use standard culture/harvest techniques as for karyotyping any solid tissue. You can collect more mitotic cells by increasing the time (and perhaps concentration) of colcemid exposure. The overnight protocol (decreased colcemid concentration plus BrdU) seems to work well for tumor cells, usually.

@ Betty G Dunn: Madam  i have succeeded in culturing the primary breast cancer cell but now im stuck at hypotonic solution, I have treated cells with various concs of KCl  and also used detergents along with KCl as suggested by various papers but all affords gone into vain. a very few no. of plates are obtained like 5-6 metaphase plates per slide, so i need your suggestion to increase the plate number.