EMS1 AMPLIFICATION CAN OCCUR INDEPENDENTLY OF CCND1 OR INT-2 AMPLIFICATION AT 11Q13 AND MAY IDENTIFY DIFFERENT PHENOTYPES IN PRIMARY BREAST-CANCER

Chromosome 11q13 is amplified in about 13% of primary breast cancers, CCND1, encoding the cell cycle regulatory gene cyclin D1, and EMS1, en coding a filamentous actin binding protein, are favoured candidate ono cogenes, whereas INT-2 is an unexpressed gene at this locus. In this s tudy we tested the possibility that different regions of this large am plicon could be independently amplified and subsequently defined the p henotype of EMS1 amplified tumours in a series of 961 primary breast c arcinomas. Using DNA slot blots, EMS1 was amplified in 15.2% of sample s: 5.4% were coamplified for CCND1; 7.9% coamplified for INT-2 and 6.7 % showed EMS1 amplification alone. The degree of amplification of CCND 1 and INT-2 was highly correlated (P=0.0001). In contrast, no such rel ationship existed between EMS1 and CCND1 or INT-2 amplification, demon strating independent amplification of EMS1 in 44% of amplified tumours . EMS1 amplification (greater than or equal to twofold increase in cop y number) was positively correlated with patient age greater than or e qual to 50 years (P=0.025), ER positivity (P=0.022), PgR positivity (P = 0.018), and was negatively correlated with HER-2/neu (c-erbB2) ampl ification (P=0.01). In common with CCND1/INT-2, EMS1 amplification was associated with increased risk of relapse in patients with lymph node -negative disease (P=0.028). In contrast, EMS1 and CCND1/INT-2 amplifi cation appeared to confer different phenotypes in ER positive and nega tive tumours. A greater than or equal to threefold increase in EMS1 co py number was associated with an apparent increased risk of relapse an d death in patients with ER negative tumours, but was without effect i n ER positive tumours. In contrast, CCND1/INT-2 amplification had no e ffect in the patients with ER negative tumours but was associated with early relapse in ER positive patients. Thus EMS1 amplification may id entify subgroups of breast cancer patients with increased probability of relapse and death distinct from those identified by CCND1/INT-2 amp lification. Further studies are required to more clearly determine the functional consequences of EMS1 overexpression and a biological basis for the relationship between EMS1 amplification and phenotype in brea st cancer.