Modelling of tumour repopulation after chemotherapy.

While repopulation is a clinically observed phenomenon after radiotherapy, repopulation of tumour cells between cycles of chemotherapy is usually a neglected factor in cancer treatment. As the effect of both radiotherapy and chemotherapy on tumour cells is the same (attack on cancer cells), the response of the tumour to injury and cell loss from the two treatment methods should be similar, including repopulation. Cell recruitment is known to be a possible mechanism responsible for tumour regrowth after radiotherapy. The literature data regarding mechanisms of repopulation after chemotherapy is very limited. The current paper employs a Monte Carlo modelling approach to implement the pharmacokinetics of a widely used drug (cisplatin) into a previously developed virtual head and neck tumour and to study the effect of cisplatin on tumour regression and regrowth during treatment. The mechanism of cell recruitment was modelled by releasing various percentages (5-50%) of quiescent cells into the mitotic cycle after each chemotherapy cell kill. The onset of repopulation was also simulated, with both immediate onset and late onset of cell recruitment. Repopulation during chemotherapy, if occurring, is a highly potent phenomenon, similar to drug resistance, therefore it should not be neglected during treatment.