PYY and cancer: For example, it is fundamental to learn whether the expression of YR is essential or not for the viability of tumor cells; treatments against metastatic and angiogenic mechanisms and those increasing the chemosensitivity of cancer cells must also be studied and potentiated; the expression of NPY/PYY/PP and their receptors as biomarkers and prognostic factors in cancer must be fully confirmed; and studies focused on single nucleotide polymorphisms must be performed.