A lymphoblastoid cell line from the same patient is resistant to MMC. The myeloid cell line (UoC-M1) was exposed to MMC as was the lymphoblastoid cell line (4081) derived from the same patient. Although the UoC-M1 cell line consistently demonstrated radial formation in excess of 20% (mean = 29%) in multiple experiments (left bar), the 4081 cell line was resistant (P = .003) to chromosomal breaks and radial formation after exposure to MMC (right bar). Treatment with DEB showed a similar difference. Error bars represent ± SD. *P = .003; M indicates myeloid; L, lymphoid.