1. A non-transitory computer-readable storage medium storing computer executable instructions that when executed by a computer control the computer to perform a method for classifying a region of cancerous tissue, the method comprising: accessing an image of a region of cancerous tissue; constructing a cell graph (CG) of the image, where a node of the CG includes a cluster of nuclei, and where the probability that a first node in the CG will be connected to a second node in the CG is based on a probabilistic decaying function of the Euclidean distance between the first node and the second node; decomposing the CG into a set of disconnected subgraphs I, where I={G 1 , G 2 ,. .. G m }; computing a Hosoya Index Z(G m ) for a subgraph G m , where Z(G m )≧0, and where Z(G m ) is defined as the number of subsets of a set of edges E(G m ) in which no two edges in G m are adjacent; upon determining that Z(G m ) is within a range, assigning Z(G m ) to a bin associated with the range; constructing a histogram of Z(G m ); and controlling a computer aided diagnosis (CADx) system to classify the image based, at least in part, on the histogram.