The International Agency for Research on Cancer of the World Health Organisation (WHO) has been researching the possible carcinogenic effects of various substances and environments based on scientific evidence since the 1970s. To date, IARC has evaluated almost 900 substances, compounds or environments.
    In October 2001, the IARC classified mineral wool insulation in Group 3 (formerly 2B). Group 3 means "unclassifiable as to its carcinogenicity to humans". The classification means that there is no evidence to classify mineral wool as carcinogenic. The positive reclassification of mineral wool was a result of new scientific results and comprehensive research carried out over the last 10 years by the WHO Agency for Research on Cancer in co-operation with several scientists.
    This result confirmed confidence in the safety and efficacy of mineral wool insulation.  In Europe, mineral wool insulation producers are regulated by, and comply with, the EU Directive 97/69/EC, which establishes beyond doubt the safety of the products in manufacture and use.  

IARC classifications and examples:
Group 1: Confirmed human carcinogen, e.g. tobacco smoke, asbestos, benzene, silica (crystalline)
Group 2A: Probable human carcinogen, e.g. ultraviolet radiation, diesel engine exhaust
Group 2B: Possible human carcinogen, e.g. coffee, urethane, dry-cleaning solutions
Group 3: Carcinogenic properties not classifiable, e.g. tea, several plastics, glass filament,  silica (vitreous), saccharin, mineral wool
Group 4: Probable human non-carcinogen, only one  substance, 'caprolactam'.

Source:PAROC GROUP