The photoacoustic tomography by using the handheld probe has a great potential in clinical breast imaging. However, the shape of the probe limits the choice of light delivery in this setup. In this letter, we study two commonly used illumination types for handheld probe: bright-field illumination and dark-field illumination. Our results demonstrate several parameters have important impact on the photon fluence in deep breast tissue. The results will help to optimize the design of the photoacoustic breast imaging system with a handheld probe.