Elastica–van Gieson-based periarterial/perivenous invasion and periductal invasion as differential predictors of lymph node metastasis after neoadjuvant chemotherapy in invasive breast carcinoma of no special type

Background/objectives Periarterial/perivenous invasion (periA/V) on Elastica-van Gieson (EVG) staining is a highly sensitive histological marker of lymph node metastasis (LNM) in invasive breast carcinoma of no special type (IBC-NST) without neoadjuvant chemotherapy (NAC), but its value after NAC remains unclear. We evaluated periA/V and periductal invasion (periD) as LNM predictors according to histological therapeutic effect.Methods We retrospectively analyzed 108 patients with residual IBC-NST after NAC, stratified into good-response (n = 44) and poor-response (n = 64) groups. LNM was defined as N0(i+), N1mi, or N1-3. Associations were assessed by Fisher's exact test and conventional or Firth logistic regression. Multivariate models included pathological T category and, in the overall cohort, histological therapeutic effect.Results LNM was present in 56 (51.9%) patients. In the overall cohort, periD (odds ratio [OR], 3.65; 95% confidence interval [CI], 1.26-10.60) and ypT2-4 (OR, 2.97; 95% CI, 1.02-8.64) were independently associated with LNM, whereas periA/V and histological therapeutic effect were not. In good responders, periD showed a borderline multivariate association (OR, 5.75; 95% CI, 0.955-60.675; p = 0.056), with high specificity (96.3%) and positive predictive value (83.3%). In poor responders, periA/V remained independently associated with LNM (OR, 6.67; 95% CI, 1.14-69.97; p = 0.034), with high sensitivity (97.4%) and negative predictive value (90.0%).Conclusions Associations of EVG-based parameters with LNM differed by histological therapeutic effect: periD showed a borderline association in good responders, whereas periA/V remained independently associated in poor responders, suggesting complementary roles in post-NAC risk stratification.