The present invention provide pharmaceutical compositions containing a pyrylium compound, a thiopyrylium compound, a selenopyrylium compound or a telluropyrylium compound or a salt of any of the aforesaid compounds as active ingredient. The compounds are selectively absorbed by cancer cells or similar growths in the human or animal body and can be used to bring about distruction of the unwanted growth on irradiation with light of wavelength 600 nm to 1000 nm. The invention also provides a method for the treatment of the human or animal body which comprises administering the compound to a human or animal and irradiating a locus in said animal where the compound is absorbed in order to kill cells at that locus. It further comprises the use of the aforesaid compound for the making of a medicament for use in the treatment of cancer in humans and animals.