Evaluation of a Patient With Non-Myoinvasive Uterine Serous Carcinoma Confined to a Polyp and Positive Peritoneal Washings With Somatic ARHGAP35 and KRAS Mutations.

Currently, the application of peritoneal washings as a diagnostic tool for endometrial cancer staging is not well defined. The case described aims to highlight the current ambiguity surrounding the use of peritoneal washings in clinical practice.  A 69-year-old G3P3003 presented to her gynecologist with complaints of new-onset heavy vaginal bleeding. The patient sought an endometrial biopsy, which suggested serous endometrial intraepithelial carcinoma (EIC) focally suspicious for invasive carcinoma, with the involvement of polyps. Based on these results, a robotic-assisted total laparoscopic hysterectomy, bilateral salpingo-oophorectomy, bilateral sentinel lymph node dissection, and omentectomy were performed. Results from her final pathology exhibited a stage IA uterine serous carcinoma (USC) involving a polyp (4.2 cm in greatest dimension) with no myometrial or lymphovascular invasion, but washings were positive for adenocarcinoma. Based on her family history of malignancy, the patient underwent germline panel testing. The patient's somatic tumor testing demonstrated proficient DNA mismatch repair status, microsatellite stability, low tumor mutational burden (4 mut/Mb), low loss of heterozygosity (9%), amplification of the ERBB2 (HER2/neu) gene by both immunohistochemistry (3+, 20% positive) and fluorescence in-situ hybridization. Her tumor also had weakly positive estrogen receptor expression (1+, 10% positive); furthermore, some pathogenic variants in KRAS (c.37G>T), PIK3CA (c.263G>A), and TP53 (c.743G>A) were identified. Given the incongruent findings found with the positive peritoneal washing and negative lymph node involvement in addition to molecular testing, management for this patient was unclear. Ultimately, this case highlights a number of advances within the field of gynecological oncology but also emphasizes the persistent ambiguity and incongruency in the management of patients with early-stage high-risk histologies. Moving forward it will become increasingly important to be able to develop a more standardized process to assess how these diagnostic tools should inform prognosis and treatment plans.