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Breast

E62: Upstaging from cT1 to pT2 in Triple Negative and Her2 Positive Breast Cancer: an Opportunity to Identify cT1 Breast Cancer Patients for whom Neoadjuvant Chemotherapy Should be Considered

Introduction: The use of neoadjuvant chemotherapy (NAC) is considered for all subtypes of breast cancer (BC) ≥T2 or > N0. In triple negative (TN) and Her2 positive (Her2+) BC cases, this decision is also driven by the availability of adjuvant therapies for patients with residual disease post NAC, which have been shown to impact survival. Primary surgery is the standard approach for cT1N0 TN and Her2+ BC. However, pathologic stage may be discordant with clinical stage, revealing pT2 or higher that would have benefited from NAC had they been identified as cT2. We aim to define the rate of cT1 to pT2 upstaging at our institution in TN or Her2 + BC undergoing primary surgery. Secondarily, we aim to identify any clinicopathologic factors that may predict cT1 to pT2 upstaging to better identify cT1 cases in which NAC should be considered.

Methods: Our institutional IRB approved prospective breast cancer database was queried for all cT1N0 TN or Her2+ cases undergoing primary surgery from 2016 to 2021. Patient demographics, clinical characteristics, tumor biology, and clinical/pathologic staging were recorded. Univariate odds ratios and corresponding 95% Confidence intervals were assessed using logistic regression to examine associations with pT2. All analyses were performed using SAS 9.4.

Results: We identified 335 cases, 38 were excluded by defined criteria, leaving 297 for analysis. Based on diagnostic breast imaging, 17 were cT1a, 91 were cT1b, and 189 were cT1c. Forty cases (13.5%) were upstaged from cT1 to pT2. Of these 40, 34 (85%) were cT1c, 27 (66%) of these cT1c cases were ≥ 15 mm based on preoperative imaging. On univariate analysis, the only significant predictor of pT2 upstaging for the entire population was size (< 0.001). Biology, breast density and imaging modality were not significant predictors of pT2 upstaging. Using a threshold for cT1 cases of < 15 mm rather than ≤20 mm for primary surgery in our population would have resulted in a 4.4% pT2 upstage rate.

Conclusions: Improved identification of the cT1 TN or Her2+ BC cases that are likely to upstage to pT2 is critical, as it has the potential to significantly affect survival outcomes due to the known benefit of NAC for T2 cases. In our population, utilizing a cT1 size threshold of < 15 mm for upfront surgery would result in a lower rate of upstage to pT2 (4.4% versus 13.5%). This highlights the importance of consideration of NAC for cT1c cases ≥ 15mm as it may have significant clinical implications on patient outcomes. Further studies to better predict T-stage in cT1c cases ≥ 15mm are needed.

Learning Objectives:

  • Describe the current clinical size threshold for neoadjuvant chemotherapy in triple negative and Her2+ breast cancer.
  • Recognize that a subset of patients may be upstaged on final pathology.
  • Define the characteristic that increases the likelihood of upstaging.