A method of determining the presence or absence of, or response to therapy against, an ovarian cancer in a woman, said method comprising the steps: • providing a biological sample from said woman, said sample comprising cell-free DNA of said woman; and • determining, in at least one molecule of said cell-free DNA, the methylation status at one or more CpGs located within one or more of the nucleotide sequences independently selected from the group consisting of: SEQ ID Nos: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 and 31, or an allelic variant and/or complementary sequence of said nucleotide sequence(s), wherein at least one of said nucleotide sequences is SEQ ID NO: 3 or an allelic variant and/or complementary sequence of said nucleotide sequence, and the methylation status at two or more CpGs located within said nucleotide sequence of SEQ ID NO: 3 is determined; wherein, the presence in at least one of said cell-free DNA molecules of two or more methylated CpGs located in the nucleotide sequence of SEQ ID NO: 3 and optionally one or more: (i) methylated CpGs associated with one or more of said nucleotide sequences independently selected from: SEQ ID NOs: 1, 2, 4, 10, 12, 14, 15, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29 and 30; and/or (ii) un-methylated CpGs associated with one or more of said nucleotide sequences independently selected from: SEQ ID NOs: 5, 6, 7, 8, 9, 11, 13, 16, 17, 22 and 31, indicates the presence of, or a reduced response to therapy against, an ovarian cancer in said woman, preferably wherein said biological sample is liquid biological sample selected from the group consisting of: a blood sample, a plasma sample and a serum sample. • providing a biological sample from said woman, said sample comprising cell-free DNA of said woman; and • determining, in at least one molecule of said cell-free DNA, the methylation status at one or more CpGs located within one or more of the nucleotide sequences independently selected from the group consisting of: SEQ ID Nos: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 and 31, or an allelic variant and/or complementary sequence of said nucleotide sequence(s), wherein at least one of said nucleotide sequences is SEQ ID NO: 3 or an allelic variant and/or complementary sequence of said nucleotide sequence, and the methylation status at two or more CpGs located within said nucleotide sequence of SEQ ID NO: 3 is determined; wherein, the presence in at least one of said cell-free DNA molecules of two or more methylated CpGs located in the nucleotide sequence of SEQ ID NO: 3 and optionally one or more: (i) methylated CpGs associated with one or more of said nucleotide sequences independently selected from: SEQ ID NOs: 1, 2, 4, 10, 12, 14, 15, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29 and 30; and/or (ii) un-methylated CpGs associated with one or more of said nucleotide sequences independently selected from: SEQ ID NOs: 5, 6, 7, 8, 9, 11, 13, 16, 17, 22 and 31, indicates the presence of, or a reduced response to therapy against, an ovarian cancer in said woman, preferably wherein said biological sample is liquid biological sample selected from the group consisting of: a blood sample, a plasma sample and a serum sample.