An in vitro method for the differential diagnosis of a malignant ovarian tumor, wherein said malignant ovarian tumor is a malignant tumor in ovaries which can be serous, mucinous, endometrioid, clear cell tumor, or undifferentiated tumor, from a benign or in situ ovarian tumor or from a benign non-tumoral ovarian lesion, in a subject, selected from Method and Method, wherein A) Method comprises: detecting the presence of proCOL11A1 protein in a sample obtained by means of biopsy, cytology or surgical resection from said subject wherein - the detection of the presence of proCOL11A1 protein in said sample is indicative that the ovarian tumor is malignant; or, alternatively - the non-detection of the presence of proCOL11A1 protein in said sample is indicative that the ovarian tumor is benign or in situ, or that the subject has a benign non-tumoral ovarian lesion; and B) Method comprises: - comparing the expression level of the proCOL11A1 protein in said sample with the expression level of said proCOL11A1 protein in a control sample; wherein - an expression level of the proCOL11A1 protein in said sample greater than the expression level of said proCOL11A1 protein in a control sample is indicative that the ovarian tumor is a malignant tumor, or, alternatively - an expression level of the proCOL11A1 protein in said sample equal to or less than the expression level of said proCOL11A1 protein in a control sample is indicative that the ovarian tumor is benign or in situ, or that the subject has a benign non-tumoral ovarian lesion. A) Method comprises: detecting the presence of proCOL11A1 protein in a sample obtained by means of biopsy, cytology or surgical resection from said subject wherein - the detection of the presence of proCOL11A1 protein in said sample is indicative that the ovarian tumor is malignant; or, alternatively - the non-detection of the presence of proCOL11A1 protein in said sample is indicative that the ovarian tumor is benign or in situ, or that the subject has a benign non-tumoral ovarian lesion; and - the detection of the presence of proCOL11A1 protein in said sample is indicative that the ovarian tumor is malignant; or, alternatively - the non-detection of the presence of proCOL11A1 protein in said sample is indicative that the ovarian tumor is benign or in situ, or that the subject has a benign non-tumoral ovarian lesion; and B) Method comprises: - comparing the expression level of the proCOL11A1 protein in said sample with the expression level of said proCOL11A1 protein in a control sample; wherein - an expression level of the proCOL11A1 protein in said sample greater than the expression level of said proCOL11A1 protein in a control sample is indicative that the ovarian tumor is a malignant tumor, or, alternatively - an expression level of the proCOL11A1 protein in said sample equal to or less than the expression level of said proCOL11A1 protein in a control sample is indicative that the ovarian tumor is benign or in situ, or that the subject has a benign non-tumoral ovarian lesion. - comparing the expression level of the proCOL11A1 protein in said sample with the expression level of said proCOL11A1 protein in a control sample; - an expression level of the proCOL11A1 protein in said sample greater than the expression level of said proCOL11A1 protein in a control sample is indicative that the ovarian tumor is a malignant tumor, or, alternatively - an expression level of the proCOL11A1 protein in said sample equal to or less than the expression level of said proCOL11A1 protein in a control sample is indicative that the ovarian tumor is benign or in situ, or that the subject has a benign non-tumoral ovarian lesion.