-This work proposes a hybrid segmentation method based on Morphological Operators and on a Gaussian function constraint to delimitate the search dominium, both used for tumor segmentation purposes The Watershed operator was also used to find tumor contour. The proposed method was firstly evaluated using gear simulated images (eight and sixteen teeth with different width and height), a power speckle noise of 10% and a contrast ratio of 10:53 referred to the background. The hybrid method was also applied to 200 ultrasound (US) breast images. For assessing the segmentation performance, similarity parameters (overlap ratio, RS, normalized residual mean square value, nrv, and mean distance between contours, dmed) based on the predefined shape or on the US tumor contour depicted by an expert as a gold standard. The segmented contour of the gear simulated images obtained with the hybrid method better preserves the original shape. This finding was evident for both gears, which is particularly important since the teeth mimic contour irregularities. For the US breast images, the proposed method keeps the tumor boundaries without aggregating improper structures, resulting in RS > 50% for 91% of the images, nrv < 40% for 70%, and dmed < 5 pixels for 77% of the cases. These findings suggest that the hybrid method represents more realistically tumor contours, which is a vital diagnosis characteristic.