4-6 cores using a 14-16 gauge needle is probably ideal- the critical thing being the tumour content.25,26 Ideally the lab needs at least 1000 cells of which 30% are tumour, but the more the better1,27. If multiple cores are taken and blocks made, an H&E with unstained sections should be sent from the block that is best fixed with highest tumour volume and percentage27

Formalin penetrates tissue at approximately 1mm per hour, so optimal fixation depends on the thickness of the biopsy, however as a broad rule, biopsies should not remain in fixative for longer than 24 hours and resection (large surgical) specimens longer than 48 hours26,27

Yes as long the cytology sample is spun down and processed into a formalin fixed paraffin embedded block and contains a sufficient amount of tumour cells it is likely to be suitable for molecular testing26,27

A post neo-adjuvant chemotherapy sample is likely to contain damaged and necrotic tissue elements and so is likely to present a challenge, this is why a biopsy sample prior to chemotherapy is preferred, however if it is the only available material it may still facilitate a result1

The testing lab should report a test within 4 weeks of receipt of the slides1. If a test fails the laboratories should contact each other to discuss the reason(s) and agree corrective action- details can be found on the test request form28,29