I think there is high likelihood of textual error here, but taking the
sentence as written, it could be rephrased as
"Patients who had a negative test result on some other relevant test,
before receiving a result of "vCPS < 5%" or "not evaluable" on the PD-L1
test, account for approx. 40% of the patients in the combination
treatment arm, and such patients would not be affected (by the exclusion
criteria in question) and will be given the study treatment."
It would sort of seem more logical if "PD-L1 vCPS < 5%/not
evaluable" was the false negative result, in which case the word
"before" does not make sense:
"Patients with a false negative result on PD-L1 of vCPS < 5%/not
evaluable, reaching ~40% in the combination treatment arm, would be not
affected and will be given study treatment."
However, I don't know anything about the broader context or what the
author actually intended, beyond the general knowledge that a PD-L1 test
is a test that is predictive of the efficacy of certain types of
anticancer immunotherapies, and CPS < 5%/not evaluable would be a low or
negative score on this test, suggesting that therapies which target
PD-L1 would not be effective in such a patient (unless the result in
question was a false negative).
In terms of a Japanese translation based on the above two
interpretations, maybe the following would be a possibility:
PD-L1
vCPS<5%/評価不能(となる以前)で偽陰性の結果が出た患者は、併用療法アームで約40%に達するが、該当しないものとして、試験治療が施されます。
Herman Kahn