Crawling wave (CrW) sonoelastography is an elasticity imaging technique capable of estimating the localized shear wave speed in tissue and, therefore, can provide a quantitative estimation of the Young's modulus for a given vibration frequency. In this paper, this technique is used to detect cancer in excised human prostates and to provide quantitative estimations of the viscoelastic properties of cancerous and normal tissues. Image processing techniques are introduced to compensate for attenuation and reflection artifacts of the CrW images. Preliminary results were obtained with fifteen prostate glands after radical prostatectomy. The glands were vibrated at 100, 120 and 140Hz. At each frequency, three cross-sections of the gland (apex, mid-gland and base) were imaged using CrW Sonoelastography and compared to corresponding histological slices. Results showed good spatial correspondence with histology and an 80% accuracy in cancer detection. In addition, shear velocities for cancerous and normal tissues were estimated as 4.75±0.97 m/s and 3.26±0.87 m/s, respectively.