Allergic disorders Allergy such as asthma eczema hay fever allergic rhinitis and food allergies are common health problems around the world and as a result of immune system response to innocuous environmental antigens which is mainly mediated by TH2 response In contrast to TH2 cells TH1 cells produce pro inflammatory cytokines and are the major player in immunity against infections eliminating cancerous cells as well as autoimmune disorders 1 Imbalance of these Th1 Th2 pathways is responsible for multiple immunological disorders including allergies autoimmune disorders and hypersensitivity reactions consequently manipulating and deviation one pathway toward the other is a promising strategy for management of many immune associated disorders although there are some controversies 1 4 As the TH1 and TH2 cells down regulate each other over activation of one system may exacerbate or relieve symptoms In this regard inverse relationship between atopic dermatitis AD and insulin dependent diabetes mellitus as well as different cancers reported 5 At the moment there is controversy about the relationship between allergy and cancers
Studies published before 1985 provided evidences for reduced risk of cancer in allergic diseases 19 Finding of epidemiological studies since 1980s are more complicated implicating that the association might rely on both particular Allergy and specific organs In this review we discuss the existing data on the association between Allergy and different type of cancers A critical evaluation of the literature in this matter is essential to clarify previous controversial findings and to determine future research directions Hematological malignancies Allergy has been assessed as protective factors for several cancers including childhood leukemia Evaluation of 1842 children with acute lymphoblastic leukemia ALL disclosed that a history of eczema correlated with a significant reduced risk for cancer odds ratio OR 0 7 95 CI 0 5 to 0 9 in a case control study in the USA 20 Also history of AD was related with significantly 50 lower risk for ALL and not significantly 20 decrement in the risk of acute myeloid leukemia AML 21 Controversy a study including 180 childhood
ALL patients in Taiwan demonstrated no significant association of childhood ALL with history of eczema OR 1 1 95 CI 0 6 to 2 0 22 Studies evaluating association in adult leukemia have mixed results A non significant risk of chronic lymphocytic leukemia CLL in adults with a history of eczema was announced in USA population 23 A case control record and population based study reported that any allergy and asthma was related with an greater odds of childhood ALL 24 Specifically in a meta analysis performed in 2010 on childhood adolescent ALL the risks of atopy allergies asthma hay fever and eczema were 0 7 0 8 0 5 and 0 7 95 CI 0 5 to 0 9 95 CI 0 6 to 1 0 95 CI 0 4 to 0 5 and 95 CI 0 6 to 0 9 respectively 8 Recently a cohort population based study in UK revealed that atopy is linked with a 50 lower risk of CLL relative risk RR 0 5 95 CI 0 3 to 0 8 25 Hodgkin lymphoma HL malignancy of B cell is one of the most prevalent cancers in younger adults 26 It has been proposed that Allergy might be related with an increased risk of HL particularly in younger cases 27 It has reported that history of allergic rhinitis was correlated with a non significantly lower risk of HL OR 0 8 95 CI 0 6 to 1 0 P 0 09 28 Similarly self reported of hay fever was associated with a 14 lower risk of non Hodgkin NHL in a large population based study 29 Breast cancer Breast cancer BC is the second most frequent cause of cancer related mortality among women worldwide In 1985s a study reported no association between BC risk and hay fever but the risk of BC was rather decreased in women with history of hives or other allergies 19 But in other study a history of allergies or hay fever was related with a 20 lower risk of BC 95 CI 0 7 to 0 9 30 Also among young American women an allergic condition was associated with a low risk of BC 31 Other several studies of allergies and BC risk represented no association although may not have had enough power to evaluate this association 32 34 Case control studies evaluating relationships of allergy and BCs was shown in table1
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