In Reply We thank Grimm et al and the editors for the opportunity to clarify our methods and report errata for our article.1 Using the American College of Surgeons National Cancer Database, we evaluated factors associated with upstaging in a cohort of women with a clinical diagnosis of non–high-grade ductal carcinoma in situ (DCIS) that may have been eligible for entry into active surveillance (AS) trials. We analyzed only patients with breast carcinomas classified as International Classification of Diseases for Oncology, Third Revision code 8500 (ductal histology), who were recorded in the National Cancer Database as clinical stage 0 (cTis, cN0, and cM0). To account for upstaging, we evaluated pathologic T, N, and M stage. Patients with pTis, pN0 (including pN0[i+] and pN0[mol+]), and pM0 were considered nonupstaged. Patients with pT stage greater than Tis, pN stage greater than N0, or pM stage greater than M0 were considered upstaged. Our methods differ from those used by Grimm et al; we excluded nonpurely ductal histologies and included clinical and pathologic N and M stage because nodal positivity or metastatic disease defines the presence of invasive carcinoma. We excluded 35 313 patients missing pathologic T, N, or M stage, but because of misclassification inherent in large databases, these patients showed up in small numbers in Table 3.1