Facilities must include in their audit, any cases of breast cancer among patients imaged at the facility that subsequently become known to the facility. The manner in which this information is included in the audit is left up to the facility. For example, whether to include such information in the analysis for the year in which the mammogram was originally performed or for the year when the cancer was discovered is left up to the facility. The facility’s guiding principle should be to present the information in the manner most useful to the facility. Because of the rarity of "false negatives," FDA also recommends that facilities periodically review all such cases to determine if there are any patterns to their occurrence that may only be evident by looking at more than a single year’s analysis.