Objective:To investigate the clinical and pathological characteristics, treatment and prognosis of endometriosis (EM)-associated ovarian mesonephric-like adenocarcinoma (MLA).Methods:Clinical and pathological data were collected from nine patients diagnosed with EM-associated ovarian MLA at the Obstetrics and Gynecology Hospital of Fudan University between January 2022 and December 2024. Histological slides were re-reviewed, immunohistochemical examination and molecular testing were performed, and patient follow-up was conducted.Results:(1) Clinical characteristics: the median age of the nine patients was 54 years (range: 38-69 years). All patients presented with a pelvic mass; five cases also reported abdominal pain. Tumor location included five cases in the right ovary, two in the left ovary, and two involving both ovaries. International Federation of Gynecology and Obstetrics (FIGO) staging showed 3 cases at stage Ⅰ, 4 at stage Ⅱ, and 2 at stage Ⅲ. (2) Pathological features: gross examination revealed mixed solid-cystic masses with solid areas appearing gray-white or yellow-brown; the median maximum tumor diameter was 9.0 cm (range: 2.6-13.0 cm). Microscopically, tumors exhibited various architectural patterns, including tubular, glandular, papillary, slit-like, sex cord-like, glomeruloid, and solid structures, with tubular and glandular patterns being most common. Tumor cells demonstrated mild to moderate nuclear atypia. Of the 11 tumor foci in the 9 cases, 8 showed coexistence of MLA with other tumor components, such as endometrioid carcinoma, borderline endometrioid or borderline seromucinous tumors. In 1 case of MLA mixed with a borderline endometrioid tumor, both components exhibited squamous metaplasia. Immunohistochemistry showed variable expression of GATA-binding protein 3, thyroid transcription factor-1, CD 10, and calretinin, with positive rates of 9/11, 8/11, 5/11, and 3/6, respectively. Two tumor foci (2/11) exhibited focal expression of estrogen receptor and progesterone receptor. All cases displayed wild-type p53 expression. Molecular testing via next-generation sequencing in five patients revealed pathogenic mutations in the KRAS gene (5/5), with 3 cases (3/5) harboring additional pathogenic mutations in other genes. (3) Treatment and prognosis: all patients underwent surgery, supplemented by chemotherapy and (or) targeted therapy. Five patients underwent comprehensive staging surgery, four received cytoreductive surgery, and one patient received targeted therapy. The median follow-up duration was 7 months (range: 2-27 months). Three patients (3/9) experienced recurrence, and no deaths were reported during the follow-up period. Conclusions:EM-associated ovarian MLA demonstrates diverse morphological patterns and frequently coexists with other tumor types. Accurate diagnosis relies on an integrated evaluation of histomorphology, immunohistochemistry, and molecular testing. The primary treatment for EM-associated ovarian MLA is surgery, followed by adjuvant chemotherapy. Patients harboring pathogenic KRAS p.G12C mutations may benefit from targeted therapies. Ovarian MLA is an aggressive tumor, prone to recurrence in the short term, and has a poor prognosis.

Objective:To investigate the clinical and pathological characteristics, treatment and prognosis of endometriosis (EM)-associated ovarian mesonephric-like adenocarcinoma (MLA).Methods:Clinical and pathological data were collected from nine patients diagnosed with EM-associated ovarian MLA at the Obstetrics and Gynecology Hospital of Fudan University between January 2022 and December 2024. Histological slides were re-reviewed, immunohistochemical examination and molecular testing were performed, and patient follow-up was conducted.Results:(1) Clinical characteristics: the median age of the nine patients was 54 years (range: 38-69 years). All patients presented with a pelvic mass; five cases also reported abdominal pain. Tumor location included five cases in the right ovary, two in the left ovary, and two involving both ovaries. International Federation of Gynecology and Obstetrics (FIGO) staging showed 3 cases at stage Ⅰ, 4 at stage Ⅱ, and 2 at stage Ⅲ. (2) Pathological features: gross examination revealed mixed solid-cystic masses with solid areas appearing gray-white or yellow-brown; the median maximum tumor diameter was 9.0 cm (range: 2.6-13.0 cm). Microscopically, tumors exhibited various architectural patterns, including tubular, glandular, papillary, slit-like, sex cord-like, glomeruloid, and solid structures, with tubular and glandular patterns being most common. Tumor cells demonstrated mild to moderate nuclear atypia. Of the 11 tumor foci in the 9 cases, 8 showed coexistence of MLA with other tumor components, such as endometrioid carcinoma, borderline endometrioid or borderline seromucinous tumors. In 1 case of MLA mixed with a borderline endometrioid tumor, both components exhibited squamous metaplasia. Immunohistochemistry showed variable expression of GATA-binding protein 3, thyroid transcription factor-1, CD 10, and calretinin, with positive rates of 9/11, 8/11, 5/11, and 3/6, respectively. Two tumor foci (2/11) exhibited focal expression of estrogen receptor and progesterone receptor. All cases displayed wild-type p53 expression. Molecular testing via next-generation sequencing in five patients revealed pathogenic mutations in the KRAS gene (5/5), with 3 cases (3/5) harboring additional pathogenic mutations in other genes. (3) Treatment and prognosis: all patients underwent surgery, supplemented by chemotherapy and (or) targeted therapy. Five patients underwent comprehensive staging surgery, four received cytoreductive surgery, and one patient received targeted therapy. The median follow-up duration was 7 months (range: 2-27 months). Three patients (3/9) experienced recurrence, and no deaths were reported during the follow-up period. Conclusions:EM-associated ovarian MLA demonstrates diverse morphological patterns and frequently coexists with other tumor types. Accurate diagnosis relies on an integrated evaluation of histomorphology, immunohistochemistry, and molecular testing. The primary treatment for EM-associated ovarian MLA is surgery, followed by adjuvant chemotherapy. Patients harboring pathogenic KRAS p.G12C mutations may benefit from targeted therapies. Ovarian MLA is an aggressive tumor, prone to recurrence in the short term, and has a poor prognosis.