A total of 1416 patients were diagnosed with breast cancer during the period studied with 370 cases in 2019 (control group), 341 cases in 2020, 333 cases in 2021, and 372 cases in 2022 (pandemic study groups). The percentage of breast cancers diagnosed which were metastatic at presentation was 3.8% in 2019. This significantly increased in 2022 to 14% (p ≤ 0.001). The increase in metastatic presentations in 2020 [6.5% vs 3.8% (p = 0.147)] and 2021 [6.9% vs 3.8% (p = 0.92)] as compared to 2019 were not statistically significant (Fig. 1).

Bar chart illustrating the percentage of new breast cancer patients with stage IV disease at presentation compared to stages I–III (y-axis) from years 2019 to 2022 (x-axis)

A total of 1130 patients who were consecutively surgically treated for invasive breast cancer from 2019 to 2022 were identified. This included 312 patients in 2019, 272 patients in 2020, 256 patients in 2021, and 290 patients in 2022. In 2019, 20.2% of these surgical patients underwent neoadjuvant chemotherapy (NAC). This percentage did not differ significantly in 2020 [18.4% vs 20.2% (p = 0.167)], 2021 [21.9% vs 20.2% (p = 0.7)], or 2022 [17.3% vs 20.2% (p = 0.423)].

Assessing adjuvant chemotherapy rates, 25.3% of the pre-pandemic 2019 cohort were treated with a non-significant increase in 2020 [30.2% vs 25.3% (p = 0.227)], no difference in 2021 [26% vs 25.3% (p = 0.893)], and a non-significant decrease in 2022 [20% vs 25.3% (p = 0.176)]. A similar trend was observed in adjuvant radiotherapy rates with 66.3% of patients treated in 2019. This significantly increased in 2020 [82.6% vs 66.3% (p ≤ 0.001)], did not differ in 2021 [73.4% vs 66.3% (p = 0.83)] and significantly decreased in 2022 [54.8% vs 66.3% (p = 0.005)]. When numbers of patients who underwent both adjuvant chemotherapy and radiotherapy were assessed, 20.2% of patients in 2019 had been treated. This showed non-significant increases in 2020 [26.5% vs 20.2% (p = 0.09)] and 2021 [23.8% vs 20.2% (p = 0.346)] and a significant decrease in 2022 [13.1% vs 20.2% (p = 0.027)].

The overall percentage of patients who had axillary surgery (either axillary node clearance (ANC) or sentinel lymph node biopsy (SLNB)) was 82.7% in 2019. This increased significantly during the pandemic to 90.4% in 2020 (p = 0.009) and 90.6% in 2021 (p = 0.009) and returned to pre-pandemic levels at 83.8% in 2022 (p = 0.801). Rates of ANC were 17% in 2019 and did not change significantly in 2020 [21% vs 17.3% (p = 0.365)], 2021 [21.9% vs 17.3% (p = 0.206)], or 2022 [17.3% vs 17.0% (p = 1)]. Similarly, rates of SLNB did not change significantly from 65.4% in 2019, during 2020 [69.9% vs 65.4% (p = 0.289)], 2021 [68.8% vs 65.4% (p = 0.448)], or 2022 [66.6% vs 65.4% (p = 0.829)]. These findings are summarised in Table 1.

On assessing nodal status in patients (including the NAC cohort), 34.9% of the control patients (March to December 2019) were deemed lymph node positive on pathological staging. This percentage increased during the same period in 2020 [39.9% vs 34.9% (p = 0.35)] and 2021 [40.5% vs 34.9% (p = 0.285)], but these increases did not reach significance. There was no difference in nodal positivity rates in the 2022 group compared to 2019 [33.8% vs 34.9% (p = 0.889)]. These findings are summarised in Table 2.

The pathological nodal status of patients who underwent surgery without NAC for invasive breast cancer was assessed separately with 38.2% of patients positive for nodal metastases in 2019. This showed non-significant increases in 2020 [41.1% vs 38.2% (p = 0.593)] and 2021 [44.7% vs 38.2% (p = 0.229)] and a non-significant decrease in 2022 [34.6% vs 38.2% (p = 0.506)] (Table 2). When the pathological nodal staging of only the patients who underwent NAC was assessed, 18.6% of the 2019 group were deemed node-positive. This percentage increased in the 2020 [39.5% vs 18.6% (p = 0.067)] and 2021 [31% vs 18.6% (p = 0.285)] groups without reaching significance. However, it was significantly increased in the 2022 group [18.6% vs 42.2% (p = 0.03)] (Table 2 and Fig. 2).

Bar chart illustrating the percentage of surgical patients who were lymph node positive on pathological staging after undergoing NAC in 2019 (n = 43), 2020 (n = 42), 2021 (n = 42), and 2022 (n = 45)

A total of 659 patients who were consecutively surgically treated upfront for invasive breast cancer were identified. The 175 patients in the pre-pandemic control group (March to December 2019) were separately compared to 155 patients in the first pandemic study group (March to December 2020), 158 in the second pandemic study group (March to December 2021), and 171 in the third pandemic study group (March to December 2022). The median age at diagnosis of breast cancer did not vary between the 2019 group when compared to the 2020 group [60 (31–87) vs 57 (35–85) (p = 0.170)], the 2021 group [60 vs 60 (22–84) (p = 0.791)], or the 2022 group [60 vs 60 (28–90) (p = 0.294)]. The clinical and pathological characteristics of the four groups are summarised in Table 3.

Median pathological tumour size was 0.2 cm larger in 2020 as compared to the 2019 control group; however, this difference was not statistically significant (2.6 cm vs 2.4 cm, p = 0.098). There was no difference in median tumour size between the control group and the 2021 and 2022 groups, respectively, [2.4 cm vs 2.4 cm (p = 0.791), 2.1 cm vs 2.4 cm (p = 0.34)]. The percentage of BCS performed decreased slightly in 2020 as compared to 2019 (65.8% vs 69.1%, p = 0.518), but this did not reach statistical significance. There was no difference in the percentage of BCS performed in 2021 or 2022 as compared to 2019 [70.9% vs 69.1% (p = 0.729), 70.8% vs 69.1% (p = 0.743)].

In terms of histological tumour characteristics, the 2020 group had a significantly higher percentage of grade 3 tumours as compared to 2019 (56.2% vs 42.0%, p = 0.025) and a lower percentage of grade 2 tumours (39.1% vs 55.0%). The higher percentage of grade 3 tumours in 2021 as compared to the 2019 group did not reach statistical significance (50.3% vs 42.0%, p = 0.302). There was no difference between the 2019 and 2022 groups in grade (p = 0.414). There was no significant difference between the 2019 group and the 2020 or 2022 groups in the percentage of tumours that were positive for LVI [50.3% vs 43.1%, (p = 0.190), 38.6% vs 43.1% (p = 0.458)]. However, the 2021 group did have a higher percentage of LVI as compared to 2019 (54.4% vs 43.1%, p = 0.039).

The percentage of ER positivity was lower in the 2021 group as compared to the 2019 group (84.8% vs 91.8%, p = 0.049), with no significant difference between the 2019 group and the 2020 or 2022 groups [87.0% vs 91.8% (p = 0.163), 88.2% vs 91.8% (p = 0.36)]. There was no difference between the 2019 group and any other group in the percentage of PR positivity [74.0% vs 78.8% (p = 0.31), 74.3% vs 78.8% (p = 0.45), 78.7% vs 78.8% (p = 0.27)] or HER-2 positivity [11.0% vs 7.8% (p = 0.312), 7.0% vs 7.8% (p = 0.78), 9.5% vs 7.8% (p = 0.58)]. The distribution of breast cancer subtype differed between the 2019 group and the 2020 and 2021 groups with a higher percentage of IDC and a lower percentage of ILC diagnosed in the latter [IDC, 80.0% vs 66.3% (p = 0.04), 81.0% vs 66.3% (p = 0.014); ILC, 12.9% vs 21.7%, 10.1% vs 21.7%]. The subtype distribution did not significantly differ between the 2019 and 2022 groups (p = 0.563).

The reduced percentage of early-stage breast cancers diagnosed in the 2020 and 2021 groups as compared to the 2019 group was not statistically significant [80.3% vs 84.3% (p = 0.596), 81.7% vs 84.3% (p = 0.532)]. There was no significant difference in the percentage of early breast cancers diagnosed between the 2019 and 2022 groups (88.6% vs 84.3%, p = 0.322).