  Multiple myeloma is a plasma cell cancer that leads to a dysregulated bone
remodeling process. We present a partial differential equation model describing
the dynamics of bone remodeling with the presence of myeloma tumor cells. The
model explicitly takes into account the roles of osteoclasts, osteoblasts,
precursor cells, stromal cells, osteocytes, and tumor cells. Previous models
based on ordinary differential equations make the simplifying assumption that
the bone and tumor cells are adjacent to each other. However, in actuality,
these cell populations are separated by the bone marrow. Our model takes this
separation into account by including the diffusion of chemical factors across
the marrow, which can be viewed as communication between the tumor and bone.
Additionally, this model incorporates the growth of the tumor and the
diminishing bone mass by utilizing a ``moving boundary.'' We present numerical
simulations that qualitatively validate our model's description of the cell
population dynamics.
