The present invention relates to pyrimidine derivatives of formula (I) wherein (R1)n, R3, R4a, R5b, and Ar1 are as described in the description and their use in the treatment of cancer by modulating an immune response comprising a reactivation of the immune system in the tumor. The invention further relates to novel benzofurane and benzothiophene derivatives of formula (III) and their use as pharmaceuticals, to their preparation, to pharmaceutically acceptable salts thereof, and to their use as pharmaceuticals, to pharmaceutical compositions containing one or more compounds of formula (I), and especially to their use as modulators of the prostaglandin 2 receptors EP2 and/or EP4.
