We report on the optical photomodulation properties of all-polymer planar microcavities in which the photochromic poly((4-pentyloxy-3'-methyl-4'-(6-methacryloxyhexyloxy))azobenzene) (PMA4) acts as photoresponsive cavity layer. We induce the trans-cis isomerization process of the azobenzene group by polarized 405 nm CW-laser irradiation, while the backward process is driven by unpolarized CW-laser irradiation at 442 nm. The all-optical photoisomerization process induces a remarkable in-plane anisotropic spectral shift of the cavity modes for the first and second order photonic band gaps. The spectral and intensity modulation effects for these flexible all-polymer microcavities are discussed with respect to those so far reported in literature for analogous systems.