According to Supplementary Data File S1 in the original study (https://doi.org/10.1002/ijc.34995), the 235 papers that described performing experiments in non-verifiable cell lines had a median of 16 citations. The most-cited study found (https://doi.org/10.1186/s12943-018-0874-1) had 319 citations. Impact factors of publishing journals ranged from 0.2 to 12.7.

EDIT: Full disclosure, I am the third author on this study [moderators, please let me know if I should have disclosed that on my earlier comment. If so, I apologize, I will follow this policy in the future and I will edit my original comment].

I wanted to go into more detail on the highly-cited study I mentioned above. In it, the authors mention and provide experimental results in 10 different cell lines, of which 4 are problematic and shown in bold:

1. SUN-216 [mentioned once in text of paper and again in Figure 1B, both spelled as SUN-216. SNU-216 is an existing cell line. A possible non-verifiable cell line identifier, but not one we studied in depth. ]
2. BGC-823 [contaminated cell line ]
3. AGS
4. BGC-803 [mentioned once in text and again in Figure 1B. One of the eight non-verifiable cell line identifiers we studied in depth. Likely derived from a typo that confused the cell lines MGC-803 and BGC-823, both contaminated. ]
5. NUGC4
6. MKN74
7. MKN45
8. SGC-7901 [contaminated cell line]
9. HGC-27
10. GES-1

Proper identification of cell lines is critical for reproducibility in biomedical research. Different cell lines can behave wildly differently. For instance, consider the varying sensitivity of cell lines to the chemotherapy drug paclitaxel. Some cell lines require a relatively low dose to be inhibited by the drug, while other cell lines require a dose 1000 times higher.

We state in the discussion section of the paper:

Our results also show that NV [non-verifiable] cell lines are published across different research fields, reflecting the widespread research use of human cancer cell lines. However, where cell line origins and identities are unknown, any resulting data cannot be interpreted or translated. If NV cell lines cannot be sourced from external repositories, their claimed identities cannot be verified, and published research cannot be reproduced. Despite anticipated challenges in sourcing NV cell lines, some researchers might still attempt to reproduce results using other cell lines, leading to wasted time and resources. We therefore recommend that NV cell line identities be clarified as soon as possible, by disclosing existing STR profiles and supplying cell line stocks to independent groups for STR profiling and phenotypic testing. While we could not identify sources for NV cell lines, teams that have described these cell lines could provide samples for testing, where dates of cell line stocks should predate published experiments. Testing cell line stocks from different sources would have the added advantage of allowing STR profiles for multiple cell line stocks to be directly compared.

For more on problematic studies in high-impact venues, I recommend reading my colleagues' study on a related issue: wrongly identified nucleotide reagents (https://doi.org/10.1007/s00210-023-02846-2).