Japdip is right -- there is no way to know how a biopsy for clustered microcalcifications will turn out until the tissues have been examined by a pathologist. However, I have seen general statistics that claim only approximately 20% of microcalcifications are found near cancerous tissues.
For a basic overview about breast calcifications, see this brief article located at the Susan G. Komen website: http://ww5.komen.org/uploadedFiles/Content_Binaries/806-03203a.pdf
Please let us know how things turn out for you! The odds are in your favor.
There is no way to speculate on the outcome of a biopsy. Microcalcifications, when grouped or clustered, always raise suspicion and require a biopsy. They are an indication that the breast tissue is reacting to some abnormality within the breast but this is not always due to cancer. Waiting is difficult but it's one of those necessary evils we all must endure. Kindest regards ....