- Note: twenty cigarettes is considered equivalent to one pack; the effect of non-cigarette tobacco products on the survival of patients with p16-positive oropharyngeal cancers is undefined; cigar and pipe tobacco consumption is therefore not included in calculating the lifetime pack-years; marijuana consumption is likewise not considered in this calculation; there is no clear scientific evidence regarding the role of chewing tobacco-containing products in this disease; investigators are discouraged from enrolling patients with a history of very sustained use (such as several years or more) of non-cigarette tobacco products alone