Each individual cancer cell within a cancer cell mass is unique, with its own internal cellular pathways and biochemical interactions. These interactions contribute to the functional changes at the cellular and tissue scale, creating a heterogeneous cancer cell population. Multiscale mathematical models incorporating such complex interactions can help in studying cancer progression and serve as an in silico test base for comparing and optimising various multi-modality anticancer treatment protocols. In this presentation we discuss a multiscale modelling approach using the Compucell3D framework, incorporating single cell based intracellular dynamics, the cell microenvironment and cell-cell interactions to study the growth and progression of cancer cell mass. We will then use the model to study cell-cycle-based tumour heterogeneity and analyse how it contributes to the potential chemotherapeutic drug resistance within a heterogeneous tumour.