Uterine papillary serous carcinoma (UPSC) is an infrequent but deadly form of endometrial cancer comprising 10% of cases but contributing 40% of deaths from the disease. Recurrence rates are high for this disease. Five-year survival is 55% for all patients and only 70% for stage I disease.1 Patterns of recurrence tend to be distant (extrapelvic and extraabdominal) as frequently as they are localized to the pelvis, and metastases and recurrences are unrelated to the extent of uterine disease (such as myometrial invasion). It is for these reasons that the recommended course of adjuvant therapy for this disease is systemic therapy (typically six doses of carboplatin and paclitaxel chemotherapy) with consideration for radiation to the vagina or pelvis to consolidate pelvic and vaginal control.2 This differs from early-stage high/intermediate–risk endometrioid adenocarcinomas, for which adjuvant chemotherapy has not been found to be helpful.
Because of the lower incidence of UPSC, it frequently has been studied alongside endometrioid cell types in clinical trials which explore novel adjuvant therapies. However, UPSC is biologically distinct from endometrioid endometrial cancers, which likely results in inferior clinical responses to conventional interventions. Fortunately we are beginning to better understand UPSC at a molecular level, and advancements are being made in the targeted therapies for these patients that are unique, compared with those applied to other cancer subtypes.
As discussed above, UPSC is a particularly aggressive form of uterine cancer. Histologically it is characterized by a precursor lesion of endometrial glandular dysplasia progressing to endometrial intraepithelial neoplasia (EIC). Histologically it presents with a highly atypical slit-like glandular configuration, which appears similar to serous carcinomas of the fallopian tube and ovary. Molecularly these tumors commonly manifest mutations in tumor protein p53 (TP53) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), which are both genes associated with oncogenic potential.1 While most UPSC tumors have loss of expression in hormone receptors such as estrogen and progesterone, 25%-30% of cases overexpress the tyrosine kinase receptor human epidermal growth factor receptor 2 (HER2).3-5 This has proven to provide an exciting target for therapeutic interventions.
A target for therapeutic intervention
HER2 is a transmembrane receptor which, when activated, signals complex downstream pathways responsible for cellular proliferation, dedifferentiation, and metastasis. In a recent multi-institutional analysis of early-stage UPSC, HER2 overexpression was identified among 25% of cases.4 Approximately 30% of cases of advanced disease manifest overexpression of this biomarker.5 HER2 overexpression (HER2-positive status) is significantly associated with higher rates of recurrence and mortality, even among patients treated with conventional therapies.3 Thus HER2-positive status is obviously an indicator of particularly aggressive disease.
Fortunately this particular biomarker is one for which we have established and developing therapeutics. The humanized monoclonal antibody, trastuzumab, has been highly effective in improving survival for HER2-positive breast cancer.6 More recently, it was studied in a phase 2 trial with carboplatin and paclitaxel chemotherapy for advanced or recurrent HER2-positive UPSC.5 This trial showed that the addition of this targeted therapy to conventional chemotherapy improved recurrence-free survival from 8 months to 12 months, and improved overall survival from 24.4 months to 29.6 months.5