Abstract P6-09-29: Clinicopathological characteristics and survival outcomes in invasive papillary carcinoma of the breast: A population-based study
Authors: Zheng Y-Z , Hu X , Shao Z-M 
Published: March 2017

Abstract
Background
Invasive papillary carcinoma (IPC) is defined as having papillary architecture in &gt;90% of the invasive component. The overall incidence of IPC is low, accounting for less than 1-2% of all newly diagnosed cases of invasive breast cancer. Limited data are available that contribute to a comprehensive summarization of the clinicopathological characteristics and prognostic factors that are associated with IPC. We aimed to determine the clinicopathological characteristics and prognostic factors of IPC in a large population and help physicians to acquire a better understanding of the disease and make better informed therapeutic decisions.
Methods
We identified 233,171 female patients in the Surveillance, Epidemiology, and End Results (SEER) database who had IPC (n = 524) or infiltrating ductal carcinoma (IDC) (n = 232,647). The demographics and tumour and treatment characteristics of IPC were compared to those of IDC. A Cox proportional hazards model was used to investigate the effects of baseline characteristics on disease-specific survival (DSS). We performed a 1:1 (IPC: IDC) matched case-control analysis using the propensity score-matching method. A forest plot of hazard ratios (HRs) that was used to illustrate the exploratory subgroup analyses.
Results
Generally, IPCs occurred in older women (≥50 years old) and presented with smaller sizes, lower grades, higher rates of oestrogen receptor (ER) and progesterone receptor (PR) positivity, and reduced lymph node (LN) involvement and were less likely to be treated with mastectomy than patients with IDC. The five-year DSS rates were significantly better in IPC than in IDC (97.5% vs. 93%, respectively; P &lt; 0.001). In the multivariate analysis, patients with IPC showed a DSS that was similar to that of IDC (HR = 0.556, 95% confidence interval 0.289–1.070, P = 0.079). No significant difference was observed in DSS between matched IPC and IDC groups (P = 0.085). Subgroup analyses suggested that differences in outcomes may be partially explained by differences in tumour grade, LN status, and ER and PR status between the 2 groups. Most IPCs are ER-positive tumours. When the analysis was limited to 178,755 ER-positive IPC and IDC patients (457 IPCs and 178,298 IDCs), similar results were observed.
Conclusions
This study is currently the largest analysis of IPC. We investigated a large cohort of patients with IPC and found that this rare tumour type presents unique clinicopathological characteristics and is associated with a higher rate of breast-conserving surgery and favourable prognoses than are observed in the overall IDC population. However, this advantage was diminished after we adjusted for demographic and clinicopathological factors. Therefore, patients diagnosed with this rare variant should be made aware that its biological features are not as favourable as once thought. Therapeutic decisions should not be made based solely on this rare entity and evidence-based treatment guidelines should be strictly followed. Improving our understanding of the clinical and biological features of IPC may lead to more individualized and tailored therapies for breast cancer patients.
Citation Format: Zheng Y-Z, Hu X, Shao Z-M. Clinicopathological characteristics and survival outcomes in invasive papillary carcinoma of the breast: A population-based study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-09-29.