The International Cell Line Authentication Committee has assembled a list of nearly 500 cell lines which are either contaminated with another cell line, or else whose identity was found to be wrong. You may  check whether a given cell line is listed here in the database. For example, the MDA-MB-435 cell line, which at the time of this writing was published in more than 700 research articles as an in vitro model for breast carcinoma, is in fact a melanoma cell line.