A study funded by Merck Serono (distributors of cetuximab outside of North America; CDx biomarkers for cetuximab = EGFR+ and KRAS-) found that only 44% of all bowel cancer patients in the UK received testing for KRAS mutations (test price = £120, refunded by Merck Serono).
There is, however, no mention in the article if the standard practice of care is to preclude cetuximab prescription unless KRAS status is known, but this seems to be the underlying assumption.
Also, no mention of testing rates for EGFR status (cetuximab only works in EGFR+ cancers).
So, the study (at least described by this article) gives the the testing rates for the exclusion criterion, but provides not even a mention of the testing rates for the inclusion criterion, and gives no idea of the prescription work flow.
The FDA-approved drug label for cetuximab recommends but does not require genetic testing before prescription with cetuximab, so no guidance there.
Without knowing the UK healthcare system guidelines for prescribing cetuximab it is hard to gauge the true significance of this study's findings.
I'm going to try to track down the primary source material to see if it has anything more to offer.