Cytokeratin-positive cells in PBSC collections from normal donors and patients with non-epithelial cell-derived tumors

Background It is possible that post-transplant relapse nz patients with bre ast cancer may result, ht part from residual tumor in the autologous PBSC p roduct. It is unclear from the literature what effect residual breast tumor cells have on clinical outcome and whether purging tumor. cells would be b eneficial. We hypothesized that lack of standardization of assays for detec tion of residual breast tumor. may be responsible for the inconclusive clin ical data. Methods We compared two assays routinely used for detection of cytokeratin (CK)-positive cells in stem-cell grafts, immunohistochemistry (IHC) and flo w cytometry (FCM). The patient population consisted of individuals with bre ast cancer; non-epithelial cell-derived tumors and normal donors. A rigorou s statistical model was developed for evaluation of the data. Results We found that the IHC assay out-performed the FCM assay Importantly , both assays detected CK-positive cells in PBSC collections of patients wi th non-epithelial cell-derived tumors and in normal donors. No distinguishi ng morphological characteristics could be identified to differentiate poten tially malignant from non-malignant CK-positive cells. Due to the inability to distinguish title positive from false positive results, we developed a statistical model to establish a quantitative threshold to discriminate pos itive from negative samples. Among the patients tested no clinical outcome differences were detected regardless of where the threshold of CK-positive cells was set. Discussion We conclude that more stringent criteria and more specific marke rs, rather than the presence or absence of CK-positive cells, need to be es tablished to determine the clinical significance of minimal residual diseas e in autologous breast-cancer stem-cell grafts.