The aims of this study are to determine the frequency of diagnosis of atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS) at stereotaxic-guided ll-gauge vacuum-assisted breast biopsy (VABB) and to assess the rate of underestimation of these at subsequent surgical excision and follow-up. Moreover, we aimed to define clinical, radiological and histological features of nonpalpable lesions in core biopsies that predict the lesion upgrade. Retrospective review of ll-gauge VABB was performed to identify the underestimation rate of nonpalpable lesions diagnosed as ALH or LCIS at VABB. Thirteen cases of ALH and 36 cases of LCIS were sent to surgery, 29 cases of ALH and 14 cases of LCIS were sent to follow-up. The clinical, mammographic and histologic features were assessed. The correlation between mammographic BI-RADS score and histological B-c1assification for both ALH and LCIS lesions were performed by Pearson's test. Of 1,765 patients enrolled, lobular lesions (ALH and! or LCIS) occurred in 82 cases, and underestimation arose in 9 (10.9%). Two cases of underestimated ALH were upgraded to invasive lobular carcinoma and one to invasive ductal carcinoma. One case of underestimated LCIS was upgraded to ductal carcinoma in situ, two to invasive ductal carcinoma and three to invasive lobular carcinoma. The histology of the core and surgical specimens were compared. A significant difference was seen in the BI-RADS score (4-5 in 91% of underestimated lesions), and the size of the lesions (2: 1.5 em) for underestimated cases versus accurately diagnosed cases (p1.5cm, co-presence of high-risk lesions in the sample, signs of ductal involvement, high histological grading for atypia and follow-up in the other cases. Surgery is recommended in all cases of LCIS:Atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS), lesions that are also referred to under the umbrella heading of 'lobular neoplasia' (LN) (1), occur relatively infrequently in the breast. However, problems and controversies surrounding the most appropriate terminology and