New complexes of general formula (I) in which R.sub.1 and R.sub.2 together form a saturated or unsaturated polycyclic carbocyclic radical containing 7 to 12 carbon atoms, or a saturated or partially saturated mono-, bi- or tricyclic heterocyclic radical containing 5 to 11 chain members and a hetero-atom chosen from oxygen, sulphur or nitrogen, which latter atom can optionally be substituted by an alkoxycarbonyl radical, and, X.sub.1 and X.sub.2 represent chlorine atoms or together form either a radical of structure: ##STR1## in which n is 0 to 2 and R.sub.6 and R.sub.7, which are identical or different, are hydrogen atoms or, when n=1, can be alkyl radicals or form, together with the carbon atom to which they are attached, a cyclobutyl radical, or a radical of structure: ##STR2## in which n, R.sub.6 and R.sub.7 are defined as above, or their salts where such exist, and their hydrates, their preparation and the pharmaceutical compositions which contain them. ##STR3##

Preparation of a lipophilic platinum complex being dissolved or suspended in an iodized poppyseed oil fatty acid ethyl ester is useful as an agent for treatment of cisplatin-resistant cancers.

A platinum complex having a superior antitumor activity is disclosed. The platinum complex has a structure represented by the formula: ##STR1## wherein A and B independently represent a lower alkanoyloxy group which may have a halogen atom substituent, or in combination represent a group: ##STR2## wherein R.sub.1 and R.sub.2 independently represent a hydrogen atom, a hydroxyl group, or a lower alkyl group, or in combination with each other and with the adjacent carbon atom a cyclobutane ring, and R.sub.3 represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a halogen atom, a sulfo group, or nitro group.

Novel platinum(II) complexes of 1,2-diaminocyclohexane, 2,2'-bipiperidine, 1,2-diamino-2,4-dimethylpentane, 1,2-diaminocyclooctane, 3,4-diamino-2,5-dimethylhexane and 1-aminomethylcyclooctylamine are provided: such complexes are of use in inhibiting the growth of certain mammalian tumors.

This disclosure describes water soluble platinum complexes of novel malonate derivatives which possess the property of inhibiting the growth of tumors in mammals.