[Risk of stage underestimation of breast cancer by sentinel lymph node biopsy method].

Sentinel lymph node (SLN) biopsy is fast becoming the standard for testing lymph node involvement in many institutions. However questions remain as to stage underestimation. The aim of this study was to analyse this specific risk in a retrospective study. Between 1975 to 1999, 1,636 patients underwent a breast cancer excision and an axillary lymph node dissection (ALND) for 437 T0, 766 T1 or 433 T2 < or = 30 mm breast cancer without axillary lymph node involvement (NO). We analyse this population because of similar characteristics with SLN biopsy present indication. Node involvement rate was analysed regarding predictive factors of lymph node involvement (LNI): pathologic diameter, grading, peritumoral vascular embols, hormonal receptors, menopause and age. Risk of no adjuvant chemotherapy indication in case of SLN biopsy method using was analysed for pre and post menopaused women. Overall lymph node involvement was 27% (444/1,636): 17% for TO stage (74/437), 26% for T1 stage (202/766), 39% for T2 < or =30 mm stage (168/433). LNI was similar for ductai and lobular invasive breast cancer respectively 27,4% (308/1,125) and 24,3% (52/214). On the other hand LNI rate was sign lower for tubular, medullar and colloids cancers: 15% (20/155). Univariate and multivariate statistical analysis showed LNI significative predictive factors: vascular embols, grade III, age < or = 50 years, tumor diameter > 30 mm. Lymph node involvement rate was defined regarding grading, vascular embols and tumor diameter with increasing rate according to different sub-groups. Among pre-menopaused patients with a false negative rate of SLN of 5%, SLN biopsy without ALND give a specific risk of wrong non-adjuvant chemotherapy indication of 1,4 case/1,000. Among menopaused patients SLN biopsy without ALND give a specific risk of 0,93 cases/1,000. Expected LNI regarding major predictive factors (vascular embols, grading and tumor diameter) allows SLN biopsy risk/benefit evaluation in different sub-groups. SLN biopsy indication could he improved according these data which could be obtain pre-operatively by micro-biopsy.