The MC38 cell line was derived from a female C57BL/6 mouse, as cited in Cancer Res 1975, 35(9): 2434-2439. The MC38 cell line was obtained from the laboratory of James W. Hodge and Jeffrey Schlom, National Cancer Institute/NIH. The STR profile is listed in the product datasheet:
https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/142/121/scc172-dat-mk.pdf
Please see the following link to review data available at Cellosaurous - https://www.cellosaurus.org/CVCL_B288
Based on these data, the MC38-K is likely, however this cannot be confirmed.