A total of 2340 full-text or summary articles, documents, and reports were extracted from various databases. After removing duplicate articles, 440 irrelevant articles were excluded from this study. Next, 351 full-text articles were assessed for eligibility and 342 review studies were excluded from this meta-analysis. Finally, 9 studies were included in this analysis based on the inclusion and exclusion criteria.

Six studies reported the prevalence of BKV in breast cancer patients (Table 4). These studies included a total of 652 patients, with sample sizes ranging from 54 to 150. The countries in which these studies were conducted included: Morocco (One study), Australia (One study), Algeria (One study), Tunisia (One study), and Iran (Two studies). The prevalence of BK among cancer patients was zero in all primary studies except the study by Alipour et al. 2% (95% CI: 0.01–0.07) [8]. (Fig. 2). Based on heterogeneity tests, the heterogeneity between primary studies was low (I-square: 0%, Q; 2.03, P = 0.85). By combining the results of these six studies with the random effect model, the overall estimate of the prevalence of BK among breast cancer patients is 0%. Considering that the number of primary studies was low (less than 10 cases), Begg’s test was used to evaluate publication bias, and the results of this test indicate no publication bias (P = 0.005). Due to publication bias, trim and fill analysis was performed to estimate the number of possible missed studies. Based on this test, the number of two new studies has been estimated. With the addition of these two primary studies, the overall estimate of the prevalence of BK among breast cancer patients has not changed. Based on the results of the sensitivity analysis, the effect of each of the primary studies on the overall estimate was not different.

Prevalence of BK virus with a 95% confidence interval in patients with breast cancer according to initial studies and overall report

Seven studies reported the prevalence of JC virus (JCV) in breast cancer patients (Table 4). These studies included a total of 782 patients, with sample sizes ranging from 54 to 150. The countries in which these studies were conducted included: China (One study), Morocco (One study), Australia (One study), Algeria (One study), Tunisia (One study), and Iran (Two studies). The prevalence of JCV in breast cancer patients in the study by Zheng et al. [25] and Hachana et al. [24] was reported as 51% (95% CI: 42–59) and 23% (95% CI: 16–31) respectively. (Fig. 3). It should be noted that the prevalence of JC among breast cancer patients in five other primary studies was zero. Also, based on heterogeneity tests, the heterogeneity between primary studies was high (I-square: 96.48%, Q; 170.31, P < 0.001). By combining the results of these seven studies, the overall estimate of the prevalence of JC among breast cancer patients is 0%. Because of this point the number of primary studies was low (less than 10 cases), Begg’s test was used to evaluate publication bias, and the results of this test indicate no publication bias (P = 0.099). Based on the results of the sensitivity analysis, the effect of each of the primary studies on the overall estimate was not different.

Prevalence of JC virus with a 95% confidence interval in patients with breast cancer according to initial studies and overall report

Three studies reported the prevalence of polyomavirus (PyV) in breast cancer patients (Table 4). The studies included a total of 305 patients, with sample sizes ranging from 76 to 149. The countries in which these studies were conducted included: Iraq (One study), Algeria (One study), and Morocco (One study). The prevalence of PyV in breast cancer patients has been reported as follows: Gihbid et al. [28] reported a prevalence of 18% (95% CI: 11–29); Corbex et al. [29] reported a prevalence of 1% (95% CI: 0–4); and Sahibsharrif et al. [30] reported a prevalence of 16% (95% CI: 10–26). Based on heterogeneity tests, the heterogeneity between primary studies was high (I-square: 93.05%, Q; 28.80, P < 0.001). By combining the results of these three studies, the overall estimate of pyv prevalence among breast cancer patients is 11%.

Three studies reported the prevalence of Merkel cell virus (MCV) in breast cancer patients (Table 4). These studies included a total of 279 patients, with sample sizes ranging from 54 to 149. The countries where these studies were conducted included: Australia (One study), Algeria (One study), and Morocco (One study). The prevalence of MCV in breast cancer patients has been reported as follows: Gihbid et al. [28] reported a prevalence of 14% (95% CI: 8–24); Antonsson et al. [31] reported a prevalence of 2% (95% CI: 0–10); and Corbex et al. [29] reported a prevalence of 1% (95% CI: 0–4). Based on heterogeneity tests, the heterogeneity between primary studies was high (I-square: 82.69%, Q; 11.56, P < 0.001). By combining the results of these three studies, the overall estimate of MCV prevalence among breast cancer patients is 4%.

Four studies reported the prevalence of simian virus 40 (SV40) in breast cancer patients (Table 4). These studies included a total of 388 patients, with sample sizes ranging from 54 to 149. The countries in which these studies were conducted included: Australia (One study), Algeria (One study), Tunisia (One study), and Morocco (One study). The prevalence of SV40 in breast cancer patients has been reported as follows: Hachana et al. [24, 32] reported a prevalence of 0.22% (95% CI: 15–31) and in three other studies it was zero. Based on heterogeneity tests, the heterogeneity between primary studies was not high (I-square: 90.25%, Q; 30.77, P < 0.001). By combining the results of these four studies, the overall estimate of the prevalence of sv40 among breast cancer patients is zero.

Three studies reported the prevalence of human polyomavirus type 6 (HPyV6) in breast cancer patients (Table 4). These studies included a total of 279 patients, with sample sizes ranging from 54 to 149. The countries in which these studies were conducted included: Australia (One study), Algeria (One study), and Morocco (One study) (Table 4). The prevalence of HPyV6 in breast cancer patients has been reported as follows: Gihbid et al. [28] in Morocco reported a prevalence of 3% (95% CI: 1–9); Antonsson et al. [31] in Australia reported a prevalence of 2% (95% CI: 0–10); and Corbex et al. [29] in Algeria reported a prevalence of 0%. Based on heterogeneity tests, the heterogeneity between primary studies was not high (I-square: 34.37%, Q; 3.05, P = 0.22). By combining the results of these three studies, the overall prevalence of hpyv6 among breast cancer patients is 1%.

Three studies reported the prevalence of human polyomavirus type 7 (HPyV7) in breast cancer patients (Table 4). These studies included a total of 279 patients, with sample sizes ranging from 54 to 149. The countries in which these studies were conducted were Australia (One study), Algeria (One study), and Morocco (One study) (Table 4). The prevalence of HPyV7 in breast cancer patients has been reported as follows: Antonsson et al. [31] in Australia reported a prevalence of 2% (95% CI: 0–10); Gihbid et al. [28] in Morocco reported a prevalence of 1% (95% CI: 0–7); and Corbex et al. [29] in Algeria reported a prevalence of 0%. Heterogeneity testing showed no significant heterogeneity between primary studies (I-square: 1.46%, Q = 2.03, P = 0.36). By combining the results of these three studies, the overall estimate of hpyv7 prevalence among breast cancer patients is zero.

Three studies reported the prevalence of KIV in breast cancer patients (Table 4). These studies included a total of 279 patients, with sample sizes ranging from 54 to 149. The countries in which these studies were conducted included: Australia (One study), Algeria (One study), and Morocco (One study) (Table 4). The prevalence of KIV among breast cancer patients was zero in all three primary studies.

Three studies reported the prevalence of WUV in breast cancer patients (Table 4). These studies included a total of 279 patients, with sample sizes ranging from 54 to 149. The countries where these studies were conducted included: Australia (One study), Algeria (One study), and Morocco (One study) (Table 4). The prevalence of WUV among breast cancer patients was zero in all three primary studies.

Three studies reported the prevalence of TSV in breast cancer patients (Table 4). These studies included a total of 279 patients, with sample sizes ranging from 54 to 149. The countries where these studies were conducted were Australia (One study), Algeria (One study), and Morocco (One study) (Table 4). The prevalence of TSV among breast cancer patients was zero in all three primary studies.