The third-order nonlinear response of the strongly coupled cavity-exciton system shows strong signatures of the long- and short-living four-particle correlations, which manifest themselves in polarization-sensitive four-wave mixing (FWM). In particular, the long-living correlation due to the biexciton may dominate in the third-order nonlinearity of the exciton-cavity system. In presence of inhomogeneous broadening, biexciton gives rise to the oscillation in the time-integrated (TI) FWM signal at positive time delay with biexciton binding frequency, ωb, allowing one to estimate biexciton contribution to the third-order nonlinearity. However, in the strongly coupled exciton-cavity system, TI FWM measurements have been performed only in a polarization configuration that does not permit the biexcitonic contribution. We report on the observation of the biexcitonic signature in the TI FWM signal from a semiconductor microcavity with an In0.03Ga0.97As single quantum well.