The use of stereotactic vacuum breast biopsy (VABB) is increasing in clinical practice for the assessment of non-palpable mammographic lesions [^1-3]. Taking a larger volume of tissue than a standard core biopsy, VABB seems capable of "forgiving" minor targeting inaccuracies [^1-3]. That said, it is not without complication, its main one being hematoma formation [¹]. Given that VABB is performed in the outpatient setting and women are discharged within one hour after biopsy, the suspicion for hematoma formation, as well as its progression, seems crucial. Worthy to mention is that neither the volume of blood suctioned and collected in the device's bin nor its implications have ever been studied in detail.

The objective of this study is to evaluate whether the volume of blood suctioned during VABB is associated with hematoma formation and progression, patient's age and histology of the lesion. To our knowledge, this is the first study to evaluate the bleeding during VABB and its implications.

The features of the study population are depicted in Table 1. The volume of blood suctioned was positively associated with the duration of the procedure (Spearman's rho = 0.417, p < 0.001); accordingly, hematoma formation was also positively associated with the latter (p = 0.004, MWW). However, the volume of blood suctioned was not associated with patients' age, menopausal status and histopathological diagnosis.

Concerning the association with hematoma formation, cases with hematoma presented with greater volume of blood suctioned (63.8 ? 44.7 cc vs. 17.2 ? 32.9 cc; p < 0.001, MWW). Interestingly, at the logistic regression model with hematoma formation set as the dependent variable, the association with the volume of blood suctioned followed a second-order pattern, i.e.

Both coefficients of the first- and the second-order term were statistically significant (p < 0.001). The above equation yields a predicted maximum at the log-odds scale corresponding to a volume equal to 82.6 cc.

Hematoma formation is associated with greater amount of blood suctioned during VABB. Of special interest, the association between volume of blood lost and hematoma formation follows a quadratic pattern. The probability of hematoma formation seems increasing till a volume equal to 82.6 cc, at which the second-order approach predicts a maximum. Noticeably, the exact value at which the maximum has been demonstrated is rather indicative. At a clinical level, this may imply a plateau reached above approx. 80 cc, where the hematoma probability has already been maximized. Indeed, the surgeon should be alert when this crucial domain is reached, as subsequent hematoma formation may be imminent.

Another significant finding that was demonstrated by our study concerns the duration of the procedure. Longer duration is correlated with greater amount of blood lost and hematoma formation. Longer duration may indicate a more strenuous procedure, characterized by more intense pain and greater blood loss [⁴].

A limitation of the study that needs to be declared pertains to the number of cores (24 to 96) excised; this is in line with the "extended protocol" of a double-blind study previously published by our team [³]. Indeed, the number of cores seems considerably larger than that in the majority of studies excising 6 to 12 cores [³]. Given that the number of cores has not been analysed as a risk factor in this study, it should be kept in mind that the association between the amount of blood suctioned and hematoma may an indirect one. In other words, larger volume of blood suctioned or longer duration of the procedure may be surrogate markers reflecting the effect of a greater number of excised cores, the latter per se predicting increased likelihood for hematoma formation.

To our knowledge, this is the first study that provides insight into the implications of blood suctioned during the procedure. Future studies adopting a quantitative approach on the blood lost, along with other factors putatively modulating the latter, such as depth of the lesion, may provide valuable insight into the strenuousness, adverse effects and complications of VABB.

The authors declare that they have no competing interests.

All authors have read and approved the manuscript. FZ: conceived the idea, participated in the design of the study and assisted in the writing of the manuscript; TS: participated in the design of the study, performed the statistical analysis and assisted in the writing of the manuscript; FD: participated in the design of the study and evaluated critically the manuscript; DC: performed vacuum-assisted breast biopsy and evaluated critically the manuscript; GG: performed vacuum-assisted breast biopsy and evaluated critically the manuscript; NM: performed vacuum-assisted breast biopsy; PS: performed vacuum-assisted breast biopsy; IF: evaluated critically the manuscript; EP: performed vacuum-assisted breast biopsy; GF: evaluated critically the manuscript; GZ: conceived of the study, participated in its design, performed vacuum-assisted breast biopsy and has given final approval of the version to be published

We would like to thank the President of the Hellenic Anticancer Institute Dr. Efstathios Fragoulis, for the technical organization of the Breast Unit.