"Because of their avid adaptation to growth in tissue culture plates, HeLa cells are sometimes difficult to control. For example, they have proven to be a persistent laboratory "weed" and they can contaminate other cell cultures in the same laboratory, interfering with biological research. The degree of HeLa cell contamination among other cell types is unknown, because few researchers test the identity or purity of already-established cell lines. It has been demonstrated that a substantial fraction of in vitro cell lines - approximately 10%, maybe 20%, are actually HeLa cells, due to the fact that the original cells in the cell culture have been overwhelmed by a rapidly growing population derived from HeLa contaminant cells. Stanley Gartler in 1967 and Walter Nelson-Rees in 1975 were the first to publish on the contamination of various cell lines by HeLa."
And recently the TE-7 which have been used for over 20 years as an esophageal cancer model, were found to be a completely different cancer. This has led to the proposal that all cell lines be continuously tested:
"He said the best way to get scientists to comply would be to withhold research grants and publication in scientific journals unless their research used authenticated cell-lines. This verification can be achieved using a technique of DNA profiling which compares the cell-line with a list of known contaminants and can cost as little as £180 per sample. "
Paranoid or justified?