Generally, young age onset malignancies show worse prognosis, But is "young age onset" a single prognostic factor for breast cancer, has been controversial. The incidence of breast cancer according to age is different by region and races. This study purposed to know the incidence of breast cancer in younger or 35 year old (below Young age group) and its clinical characteristics, prognosis, and difference with older age onset breast cancer.

A retrospective study of consecutive 545 breast cancer patients who had been treated by our hospital from 1990 to 1999, was carried out. We investigated the ratio of 35 year old or younger breast cancer patients, age of menarche, TNM stage, histologic grades, hormone receptor status, survival rates. And compared it with counter age (> 35) group's, The significances of differences were evaluated using Student's-t test or chi-square test by variable type. Analysis were performed using SPSS software.

Younger age group patients were 62 (11.3%) among them, showed earlier menarche, worse histologic differentiation, and lower mammographic detection rate than counter group (p <0,05). There were no difference in TNM stage distribution, hormone receptor expression status according to age group (p>0,05). Young age group's 5 year overall and disease free survival rates were 83±5% and 58±8%, both were lower than counter group's 89±2% and 74±3% (p<0,05). Also age adjusted overall and disease free survival rates were worse than counter age group's.

Younger age group shows worse survival rates, have poor prognostic factors and show early relapsing rate than older age group. So we can consider "young age onset" as a poor prognostic factor in breast cancer.