The ATAC ('Arimidex', Tamoxifen, Alone or in Combination) adjuvant breast cancer trial: first results of the endometrial sub-protocol following 2 years of treatment.
BACKGROUND
Tamoxifen treatment results in a doubling of the risk of endometrial cancer after 1-2 years of treatment and a quadrupling after 5 years. Anastrozole, a third-generation aromatase inhibitor, with superior efficacy to tamoxifen, may also offer tolerability benefits in terms of effects on the endometrium.


RESULTS
A sub-protocol of the ATAC trial compared the incidence/type of intrauterine changes following treatment with these agents in a subgroup of patients (n = 285) from the main trial. After 2 years anastrozole treatment, endometrial thickness remained </= 5 mm (baseline: 3.0 mm); in patients receiving tamoxifen, endometrial thickness increased by 3.2 mm to 7.0 mm, with a similar trend in the combination group. At baseline, 26/285 patients (9.1%) had endometrial abnormalities, most commonly polyps. After 2 years the number of endometrial abnormalities appeared lower with anastrozole treatment compared with tamoxifen although these differences were not statistically significant (odds ratio: 0.44; 95% confidence interval 0.146, 1.314; P = 0.14). Most abnormalities occurred within the first year of treatment (anastrozole: 4/6; tamoxifen: 7/10; combination: 10/16; total: 21/32). Fewer patients in the anastrozole group (1.4%) required medical intervention (tamoxifen 12.5%; combination 13.6%).


CONCLUSIONS
Fewer endometrial abnormalities occurred during 2 years treatment with anastrozole compared with tamoxifen although statistical significance was not reached in this sub-protocol analysis.
Duffy
S
S
Department of Obstetrics and Gynaecology, St James' University Hospital, Leeds LS9 7TF, UK.
Jackson
T L
TL
Lansdown
M
M
Philips
K
K
Wells
M
M
Pollard
S
S
Clack
G
G
Coibion
M
M
Bianco
A R
AR
D000077384:Anastrozole; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000009:adverse effects* / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy*; D017024:Chemotherapy, Adjuvant / Q000009:adverse effects; D016889:Endometrial Neoplasms / Q000139:chemically induced; D004717:Endometrium / Q000187:drug effects* / Q000473:pathology; D005260:Female; D006801:Humans; D008875:Middle Aged; D009570:Nitriles / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D011127:Polyps / Q000139:chemically induced; D012307:Risk Factors; D013629:Tamoxifen / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D014230:Triazoles / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use
D009570:Nitriles; D014230:Triazoles; D013629:Tamoxifen; D000077384:Anastrozole