  The color dipole formulation provides an intuitive picture of hard processes
in high energy scattering. Most importantly, this approach allows one to
calculate nuclear effects in a parameter-free way. I review the relation
between the dipole approach and transverse momentum factorization and present
numerical results for open heavy flavor production in proton-proton and
proton-nucleus collisions. The cross section for heavy quark production off
nuclei is known to reflect gluon shadowing, but is also affected by higher
twist effects and by finite coherence length effects.
