The present case report suggests that when endometriosis in the bladder or intestine diagnosed; (i) FDG accumulation on PET-CT should be investigated for visual differentiation from malignancy, (ii) ER and PGR expression on biopsy sample is useful to determine the course of treatment, and (iii) oncogenic mutations, such as PIK3CA mutation affect proliferation. Here, ESR1 is linked to endometriosis.