A recent publication The impact of preoperative breast biopsy on the risk of sentinel lymph node metastases: analysis of 2502 cases from the Austrian sentinel node biopsy study group by Peters-Engl et al (full free text here) concluded that:
based on the present data, is that preoperative breast biopsy does not cause artificial tumour cell spread to the SLN, with possible negative impact on the prognosis of breast cancer.These results disagreed with those of Hansen et al in a paper titled Manipulation of the Primary Breast Tumor and the Incidence of Sentinel Node Metastases From Invasive Breast Cancer (summary here).
But go here and read what Dr. Hansen has to say about her study before you make a decision about the safety of cancer biopsy.
"This study does not link biopsy with spread [of breast cancer]," Hansen tells WebMD via email. "We have not changed our practice and do not plan to. We still prefer to perform a needle biopsy to confirm the diagnosis of cancer and then will proceed at another time to definitive surgical management."