PTEN and cancer: The causes of acquired resistance to synthesized molecules are various, for example, the acquisition of a new mutation in the molecular target (T790M EGFR) [67], masking the extracellular epitope of ErbB2 by hyaluronic acid [68], alternative pathways to support proliferation of the cancer cells (IGFR expression) [69], or loss of one of the negative regulators of PI3K/Akt survival pathway (phosphatase and tensin homolog, PTEN) [70].