https://www.highmarkmedicareservices.com/faq/partb/pet/billing.html#1
The above link provides following answer:
The Center for Medicare and Medicaid Services (CMS) Internet Only Manual (IOM) ; Pub. 100-2; Chapter 15; Section 50.4.5 provides the National guidelines on the Unlabeled Use for Anti-Cancer Drugs. These guidelines advise that an off-label usage of an Food and Drug Administration (FDA) approved drug will be considered for coverage when there are no specific contraindications and one of the following criteria is met:
A. Its usage is supported by one or more citations in at least one of the three drug compendia listed below, and the usage is not listed as "not indicated" in any of the three compendia:
American Hospital Formulary Service Drug Information
American Medical Association Drug Evaluations
United States Pharmacopoeia Drug Information (USPDI)
B. The use is supported by clinical research that appears in peer reviewed medical literature. This applies only when an unlabeled use does not appear in any of the compendia or is listed as insufficient data or investigational. Peer reviewed medical literature includes scientific, medical, and pharmaceutical publications in which original manuscripts are published, only after having been critically reviewed for scientific accuracy, validity, and reliability by unbiased independent experts. This does not include in-house publications of pharmaceutical manufacturing companies or abstracts (including meeting abstracts).