My VCaP cell has been cultured in DMEM medium (in petri dish) for over 20 days, the cell still grows very slowly. So the medium is exchanged every 2 days. The passage of the VCaP cells has not been administered. But I checked the previous paper, the doubling time of VCaP cell line is 5-6 days. The suggestive passage condition for VCaP cells is when the confluence reaches 80-100%. Thus, I am still waiting.