Fig. 2

Representation of common cancer types in MSC-based cytotherapy studies compiled in this review in comparison to global cancer incidences (clinical relevance). The most frequently targeted tumors in cancer cytotherapy studies have been ranked in descending order of worldwide cancer incidence (2012 data) [122] from left to right on the x axis. Global cancer incidence rates are depicted as solid line symbols (boxed values), while the frequencies of tumors targeted by unmodified/naïve MSC (n-MSC) or genetically modified MSC (GM-MSC; see also the “Genetically modified MSC as delivery vehicles for antitumorigenic molecules—overview and meta-analysis results” section) in experimental cancer cytotherapy (CT), as determined by our meta-analysis, are represented by black (n-MSC CT) or white (GM-MSC CT) columns, respectively. Sample sizes: N = 79/N = 67 for n-MSC- and GM-MSC-based work, respectively. For each cancer type, the difference in height between the solid line symbols and the column bars denotes the divergence in representation of global cancer incidence by CT work, with positive differences (global % > MSC CT %) signifying under-representation, and negative ones (MSC CT % > global %) over-representation of cancer incidence. For example, the two most under-represented tumors targeted by n-MSC CT are those of lung as well of liver/stomach/pancreas (HGP) (by 12.3% and 8.5%, respectively), while the most over-represented ones are those of breast and brain (difference of − 11.3 and − 8.3, respectively), see the main text (the “Relevance of preclinical cancer cytotherapy targeting to global cancer incidence” section) for further discussion. Overall, the data suggest that in order for experimental CT work to become more clinically relevant, more focus should be put on the following, under-represented tumor targets: * Hepatic/gastric/pancreatic (HGP) tumors (using both n-MSC and GM-MSC). * n-MSC-based lung cancer cytotherapy. * Colorectal cancer targeted by both n-MSC (especially UC-MSC) and GM-MSC. * Prostate cancer targeted by GM-MSC (especially UC-MSC), as well as n-MSC. * GM-UC-MSC-based brain tumor cytotherapy