The potential for needle tract seeding, whereby breast cancer cells are deposited along the path of the biopsy needle, has long been a concern regarding needle biopsies. In fact, evidence suggests that such seeding does occur 20 to 50% of the time. However, studies that have examined the question as to whether such seeding has any influence on survival have been reassuring. Apparently, most breast cancer cells transported in such a manner do not survive. Nevertheless, cases have been described in which local recurrences were found in the biopsy path and such "successful" malignant seeding has been estimated to occur approximately 0.07% of the time when surgery is followed by radiotherapy and 7% when radiation is omitted. Now a new study using animal models of breast cancer has demonstrated that core needle biopsies might influence the sites of metastasis, in addition to increasing the risk of malignant seeding.

Core needle biopsies influence metastasis

The study referenced at the beginning of this news article was designed to investigate the extent to which core needle biopsies affect cancer cell dissemination and tumor growth. The authors used two animal models of breast cancer to conduct the study: a chick embryo system and a mouse breast cancer model.
Hormone receptor negative MDA-MB-231 and MDA-MB-435 human cancer cells were grafted into the chick embryos, whereas mouse 4T1 Breast cancer cells were used in the mice to generate tumors. Core needle biopsies were performed on the tumors of half of the chick embryos and mice, while the remaining animals were left undisturbed for comparison purposes.
Both the chick embryos and the mice were found to experience significant differences in the frequency and location of metastases depending on whether the animals had been biopsied. There were differences in lung metastasis in both the chick embryos and mice, with the exception of the MDA-MB-231 chick embryos (which demonstrated no significant differences based on biopsy status). However, the biopsied MDA-MB-231 chick embryos experienced increased chorioallantoic membrane (a vascular membrane found in bird eggs) metastasis. In addition, both MDA-MB-231 and MDA-MB-435 chick embryos experienced significant differences in liver metastasis depending on biopsy status.
The authors conclude that core needle biopsies might increase the risk of metastatic dissemination, as well as influencing the sites of metastasis. The experiments also reinforce the concept of a multi-step metastatic pathway that is influenced by extrinsic factors. The clinical implications are considerable, according to the authors, and follow-up studies examining potential mechanisms and countermeasures are urgently required.