evaluation of breast tumour cell contamination in the bone marrow and leukapheresis collections by rtpcr for cytokeratin19 mrna there is considerable interest in an autologous transplantation at programme for patients with highrisk breast cancer however the issue of the incidence of occult bone marrow bm micrometastasis at diagnosis and the cancer contamination of peripheral blood stem cell pbsc collections used for haematological rescue is still debated the presence of bm micrometastasis was evaluated in bilateral bm biopsies obtained at diagnosis of 33 patients with stage iiiiia breast cancer using i a nested reverse transcriptasepolymerase chain reaction rtpcr assay for cytokeratin 19 k19 mrna ii histology and iii immunohistochemistry ihc analysis with a panel of three monoclonal antibodies the rtpcr assay only was used to determine contamination of pbsc collections obtained after priming with recombinant human granulocytecolony stimulating factor rhgcsf k19 transcripts in one or both bm samples were detected in 48 of patients at diagnosis with an overall 85 concordance with the results of ihc analysis on the other hand 56 of pcr and ihcpositive bm samples were diagnosed as normal on histological analysis 57 of patients showed k19 mrna in at least one pbsc collection the possibility to have contaminated pbsc collections was significantly higher in patients with k19 positivity in bm at diagnosis in four patients who had shown k19 positivity in bm and in pbsc collections immunoselected cd34 cells used for haematological rescue were k19negative there was a trend towards longer relapse free survival rfs in patients transplanted with k19negative pbsc collections as compared to the others in conclusion a substantial proportion of patients with highrisk nonmetastatic breast cancer present occult bm micrometastasis at diagnosis and also show cancer contamination of pbsc collections used for at these might represent a category of patients with poorer prognosis after at and possible candidates for more intensive andor alternative therapeutic regimens including at with purged pbscs