COVID-19 Outcomes Across Pandemic Phases in European Patients With Breast Cancer

Get Permission

In a study using data from the European OnCovid registry reported in the Journal of Clinical Oncology, Tagliamento et al found that the severity of COVID-19 infection in patients with breast cancer decreased during the Omicron variant phase of the pandemic. In addition, a full vaccine course (defined as double-dosed/boosted) vs no vaccination was associated with a significantly reduced risk of adverse outcomes.

The investigators stated, “Although representing the majority of newly diagnosed cancers, patients with breast cancer appear less vulnerable to COVID-19 mortality compared with other malignancies. In the absence of patients on active cancer therapy included in vaccination trials, a contemporary real-world evaluation of outcomes during the various pandemic phases, as well as of the impact of vaccination, is needed to better inform clinical practice.”

Study Details

The study compared all-cause 28-day case fatality rate (CFR-28) and COVID-19 morbidity among patients with breast cancer across the prevaccination (February 27, 2020, to November 30, 2020), Alpha-Delta (December 1, 2020, to December 14, 2021), and Omicron (December 15, 2021, to January 31, 2022) phases of the pandemic using data from OnCovid registry participants. The study also compared CFR-28 and COVID-19 severity in unvaccinated patients and double-dosed/boosted (fully vaccinated) patients using inverse probability of treatment weighting models adjusted for country of origin, age, number of comorbidities, tumor stage, and receipt of systemic anticancer therapy within 1 month of COVID-19 diagnosis.

Key Findings

The study included 613 patients diagnosed with COVID-19 across the three pandemic phases, consisting of 392 (63.9%) during the prevaccination phase, 164 (26.8%) during the Alpha-Delta phase, and 57 (9.3%) during the Omicron phase.

Analysis of CFR-28 showed comparable estimates of mortality across the three phases (13.9%, 12.2%, and 5.3%, respectively; overall P =.182). However, significant improvements in outcomes across the three phases, primarily reflecting better outcomes in the Omicron phase, were observed for:

  • COVID-19 complications (26.0%, 25.0%, 7.0%; overall P = .007)
  • Hospitalization due to COVID-19 (57.0%, 49.0%, 24.5%; overall P < .0001)
  • Receipt of COVID-19–specific therapy (59.2%, 44.1%, 20.0%; overall P < .0001)
  • Receipt of oxygen therapy (40.1%, 34.9%, 19.5%; overall P = .028).

No significant differences in intensive care unit (ICU) admissions were observed.

Among 566 patients eligible for vaccination analysis, 72 (12.7%) were fully vaccinated and 494 (87.3%) were unvaccinated. Outcomes among unvaccinated patients in the Alpha-Delta and Omicron phases were similar to those in patients in the prevaccination phase. Vaccinated vs unvaccinated patients had significantly better outcomes in CFR-28 (odds ratio [OR] = 0.19, 95% confidence interval [CI] = 0.09–0.40), hospitalization due to COVID-19 (OR = 0.28, 95% CI = 0.11–0.69), COVID-19 complications (OR = 0.16, 95% CI = 0.06–0.45), receipt of COVID-19–specific therapy (OR = 0.24, 95% CI = 0.09–0.63), and receipt of oxygen therapy (OR = 0.24,  95% CI = 0.09–0.67). The benefit of vaccination was not significant for ICU admission (OR = 0.12, 95% CI = 0.02–1.05).

The investigators concluded, “Our findings highlight a consistent reduction of COVID-19 severity in patients with breast cancer during the Omicron outbreak in Europe. We also demonstrate that even in this population, a complete [SARS–CoV-2] vaccination course is a strong determinant of improved morbidity and mortality from COVID-19.”

Alessio Cortellini, MD, PhD, of the Department of Surgery and Cancer, Imperial College London, is the corresponding author for the Journal of Clinical Oncology article.

Disclosure: The study was supported by the National Institute for Health Research Imperial Biomedical Research Center, Wellcome Trust Strategic Fund, and Associazione Italiana per la Ricerca sul Cancro. For full disclosures of the study authors, visit

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.