There is good evidence in some species, including @entity35 , that circannual rhythms are innate and can occur even under constant environmental conditions. Such circannual rhythms, e.g. in hormone levels and immune system function, may influence tumourigenesis. This prompted us to study @entity3653 ( @entity106 )-induced mammary @entity105 at different seasons of the year in female @entity35 under constant environmental conditions (photoperiod, temperature, air humidity, food). @entity106 was administered orally at a dose of 5 mg per @entity35 at the first day of the experiment and then at weekly intervals up to a total dose of 20 mg per @entity35 . @entity35 were palpated once weekly for the presence of mammary @entity5 . After 13 weeks, they were necropsied for examination of the number and size of mammary @entity5 . Age-matched groups of 36-99 @entity35 were used per experiment. When the experiment was performed twice within 2 years during the same season (spring/summer), @entity5 incidence (56 and 61%) and @entity5 burden were almost equal, indicating that data obtained in this way were reproducible. However, the same experiment performed in autumn yielded a significantly lower @entity5 incidence (34%) and @entity5 burden. When the experiment was started during winter, @entity5 incidence was similar to the spring/summer groups, but @entity5 burden was lower. The data indicate a seasonal variation in the development and growth of @entity106 -induced @entity0 in @entity35 . One possible explanation for this phenomenon may be the seasonal variation in pineal @entity2493 production and immune function previously reported in rodents under constant environmental conditions.

Seasonal influence on @entity3653 -induced mammary XXXX in @entity35 under controlled laboratory conditions.

@entity3653 :: ('CHEBI:254496', 'Chemical') :: ['7,12-dimethylbenz[a]anthracene'] @entity0 :: ('MESH:D001943', 'Disease') :: ['breast cancer'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumour', 'tumours'] @entity2493 :: ('MESH:D008550', 'Chemical') :: ['melatonin'] @entity106 :: ('MESH:D015127', 'Chemical') :: ['DMBA'] @entity35 :: ('10116', 'Species') :: ['rat', 'Sprague-Dawley rats', 'Rats', 'rats'] @entity105 :: ('MESH:D063646', 'Disease') :: ['carcinogenesis']
@entity105 :: (MESH:D063646,Disease) :: ['carcinogenesis']
