In 1967 the US 270 designation was at its maximum extent, from Pine Bluff AR to Syracuse KS. That year the Kansas DOT petitioned AASHO* to extend the US 270 designation even further:
US 270 is signposted as an east-west route, but based on that map, if AASHO* would have approved the proposed extension, it seems likely that US 270 would have been signed north-south within Kansas. However, AASHO denied the request.
About 13 years later, Kansas apparently decided they did not have any use for US 270, because in November 1980 they asked AASHTO* to eliminate that designation between Syracuse and Liberal (which is just a couple miles north of the Oklahoma border):
AASHTO did approve that request, and at the time of this writing the west terminus of US 270 is still in Liberal. On the map above, the decommissioned segment is shown as a green line, while the blue segment illustrates US 270 as it exists today. More about its current and historic endpoints can be found on the US 270 page.
*AASHO became AASHTO in 1973