FUCCI color codes cells as they express different color fluorescent proteins as they go through phases of the cell cycle. The cell cycle phase distribution of cancer cells in Gelfoam® histoculture was similar to in vivo tumors, whereby only the surface cells proliferate and interior cells are quiescent in G0/G1. In contrast, in 2D cancer-cell culture, most of the cells are always cycling. The cancer cells responded similarly to toxic chemotherapy in Gelfoam® culture as in vivo; as such, therapy is cell cycle dependent. In 2D culture, cancer cells were much more chemosensitive. These results indicate why the drug response pattern of tumors in Gelfoam® histoculture reflects what is observed in vivo.