Orphan Drug Designation: Disease Considerations
When reviewing a request for orphan drug designation, FDA considers the mechanism of action of the drug to determine what distinct disease or condition the drug is intended to treat, diagnose or prevent.Whether a given medical condition constitutes a distinct disease or condition for the purpose of orphan-drug designation depends on a number of factors, assessed cumulatively, including: Pathogenesis of the disease or condition; course of the disease or condition; prognosis of the disease or condition; and resistance to treatment. These factors are analyzed in the context of the specific drug for which designation is requested. 
During the course of reviewing a request for orphan drug designation, equipped with the most current scientific literature about a particular disease or condition, FDA may come to a new understanding about the nature of that disease or condition. Below is a list of some diseases or conditions for which FDA’s views on how it categorizes or otherwise understands the disease or condition has evolved. This is not a comprehensive list of orphan disease determinations, but reflective of some of the more common questions we receive. FDA will update this list as appropriate when it makes orphan drug designation determinations that change how we approach the disease or condition in question. For a complete list of orphan drug designations and approvals see the searchable Orphan Products Designation Database.
|Disease or Condition at issue||For the purpose of Orphan Drug Designation, what FDA considers the disease or condition to be:|
|Ovarian, Fallopian Tube, and Primary Peritoneal Cancer||FDA considers ovarian cancer, fallopian tube cancer, and primary peritoneal cancer to be one distinct disease or condition.|
|Metastatic Brain Cancer||FDA considers any primary tumor type that has metastasized to the brain to be its own distinct disease or condition. For example, breast cancer that has metastasized to the brain is a distinct disease from breast cancer.|
|Pulmonary Hypertension||FDA recognizes the five WHO classifications of pulmonary hypertension as distinct diseases or conditions.|
|Scleroderma||FDA considers systemic sclerosis to be a different disease or condition than localized scleroderma.|
|Lymphoma||FDA recognizes the WHO classifications of lymphoma as distinct diseases or conditions.|
|Familial Adenomatous Polyposis||FDA recognizes Familial Adenomatous Polyposis as a distinct disease or condition from sporadic adenomatous polyps|
|Medication-induced Dyskinesia in Parkinson’s Disease||FDA recognizes Medication-induced Dyskinesia in Parkinson’s Disease (PD) as the disease or condition. Levodopa-induced dyskinesia in PD is considered to be a subset of Medication induced Dyskinesia in PD.|
 See FDA, Orphan Drug Regulations, Final Rule, 78 Fed. Reg. 35117, 35120 (June 12, 2013).