[Problem]To provide a method for acquisition of data able to serve as an index for determining the likelihood that an ovarian endometriosis cyst is cancerous.SolutionThis data acquisition method for determining the likelihood that an ovarian endometriosis cyst is cancerous includes an iron concentration measurement step for measuring the iron concentration in the cystic fluid of the ovarian endometriosis cyst. This diagnostic device for diagnosing the likelihood that an ovarian endometriosis cyst is cancerous is provided, at a minimum, with an iron concentration measurement unit for measuring the iron concentration in the cystic fluid of the ovarian endometriosis cyst.