Comparison of aromatase mRNA expression between the following groups: (a) patients older than and those younger than 50 years of age; (b) patients who were negative and those who were positive for lymph node metastasis; (c) patients with tumor size < 2 cm and those with tumor size ≥ 2 cm; and (d) patients who were estrogen receptor (ER)-α positive and those who were ER-α negative, by histochemistry. The boxes represent the mean and the 70% confidence intervals; bars are standard deviations. The aromatase mRNA expression was significantly greater in those older than 50 years (29 ± 60) than in those younger than 50 years (14 ± 24; P = 0.0042). It was significantly greater in samples negative for lymph node metastasis (30 ± 62) than in samples positive for lymph node metastasis (13 ± 20; P = 0.010). The aromatase mRNA expression was significantly greater in the group with tumor size < 2 cm (29 ± 54) than in the group with tumor size ≥ 2 cm (22 ± 50; P = 0.042). Finally, it was significantly greater in the ER-α positive group (28 ± 59) than in the ER-α negative group (13 ± 20; P = 0.0021).