The SUM-159 cell line is a very interesting and enigmatic one that has had a number of twists and turns over the years. The primary tumor that came to the lab was from a 71 year old woman with a previous history of ovarian cancer. We isolated the cells by enzymatic dissociation as per our normal protocol and plated the cells overnight in our base medium of Ham’s F12 supplemented with 5% FBS, insulin and hydrocortisone. When I observed the cells the next day, I was surprised to see a nearly confluent monolayer of refractile cells with a spindle morphology. The cells looked like transformed fibroblasts! Indeed, when the pathology report came to the lab a few days later we were not surprised to read that the pathologist had described the neoplasm as either an anaplastic carcinoma or a sarcoma that was clearly distinct from the prior ovarian cancer. One of the practices we had established in the lab by this time was to always expose some of the culture dishes to a variety of cell culture media that we had developed, as cancer cells from different patients often did better in different media, and one of the media we had developed was a serum-free medium that was designed specifically for luminal epithelial cells. When we observed the cells from the same neoplasm cultured in the serum-free medium we were surprised to see that the cells exhibited an epithelial morphology that was very different than that of the same cells growing in serum-containing medium. Those morphological differences coupled with the pathology report prompted us to perform immunocytochemistry on these cells using a pan-keratin antibody. The results of this test, in our hands, was weak positivity of keratin, and based on that, we concluded that these cells came from an anaplastic carcinoma, and not a sarcoma. In that regard, it is perhaps not surprising that the SUM-159 cells have become most famous in the breast cancer stem cell literature. Expression profiling of SUM-159 cells by the Perou lab and others have put this cell line in the claudin-low subset of basal breast cancers, and they cluster very closely to the MDA-MB-231 cell line. Indeed, both of these cell lines exhibit mesenchymal features. Several labs have hypothesized that claudin-low breast cancers are derived directly from pluripotent stem cells in the breast, and SUM-159 cells exhibit all of the features of classic breast cancer stem cells. Thus, SUM-159 is a favorite of any lab that studies breast cancer stem cells, and they have appeared in many prominent papers on this subject.
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