|Fertility-sparing treatment with high-dose progestin is now used in many young patients with early stage, grade 1 endometrioid adenocarcinoma. The response rate of this therapy is quite good, but the relapse rate is relatively high. If the site of recurrence is limited to the uterus, this may be treated with additional hormone therapy or hysterectomy. We recently experienced a case of a 30-year-old primigravida patient in whom intraperitoneal dissemination of carcinosarcoma occurred during follow-up after apparent complete remission of early-stage grade 1 endometrioid adenocarcinoma. We report the case as an example of a rare high-grade histology tumor that relapsed in an extrauterine site after primary remission had been achieved with high-dose progestin therapy. In a review of the literature through a MEDLINE search, we found 13 articles describing relapse in an extrauterine site, including 6 ovarian metastases, 4 retroperitoneal lymph node metastases, and 3 metastases to organs other than the ovary. Early stage, well-differentiated endometrioid adenocarcinoma of the uterine corpus is generally considered to have a good prognosis, but counseling of patients regarding life decisions is important, with provision of sufficient information on the possibility of extrauterine progression or disseminated recurrence. Relapse as Advanced Carcinosarcoma Following Uterus-Preserving Therapy in a Patient with Early-Staged and Grade 1 Endometrioid Adenocarcinoma: A Case Report and Review of the Literature; Seiryu Kamoi, Marie Ito, Akihito Yamamoto, Atsuko Ishikawa, Takashi Yamada and Toshiyuki Takeshita.