Invasive breast carcinoma with a DCIS-like growth pattern: Clinicopathological features and diagnostic pitfalls.

Ductal carcinoma in situ (DCIS)-like invasive carcinoma is a rare morphologic pattern of expansile invasive breast cancer that is frequently misdiagnosed as ductal carcinoma in situ. However, some patients develop lymph node metastases exhibiting DCIS-like features, and there is limited literature documenting its clinicopathological characteristics. To characterize the clinicopathological features, immunophenotype, and diagnostic pitfalls of breast invasive carcinoma with a DCIS-like growth pattern (DCIS-like invasive carcinoma), a retrospective review of 319 breast carcinomas (January 2021-September 2025) identified 11 cases of DCIS-like invasive carcinoma. Clinical, histopathological, and immunophenotypic features were evaluated, and interobserver concordance for myoepithelial and basement membrane markers was assessed by 12 pathologists. Three cases (3/11, 27.27%) showed pure DCIS-like invasive carcinoma, and 8 (8/11,72.73%) were admixed with invasive carcinoma of no special type (IBC-NST). Growth patterns included cribriform, papillary, solid, and comedo and micropapillary. All tumors lacked myoepithelial marker expression (CK5/6, p63, CK14, SMA, Calponin), with Collagen IV confirming basement membrane loss; CK5/6 and CK14 showed high interobserver agreement (κ=1.00). Four patients developed axillary lymph node metastases in which the metastatic foci paradoxically retained DCIS-like morphology, directly confirming their invasive nature. Hormone receptor positivity was observed in 7(7/11,63.64%) tumors, HER2 overexpression in 2(2/11,18.18%) and the Ki-67 index ranged from 5 to 90%. With a mean follow-up of 13 months (range, 2-51 months), no local recurrence or distant metastasis was documented in 10 patients, DCIS-like morphology was identified in cervical lymph node metastasis in one patient at 51 months postoperatively. DCIS-like invasive carcinoma is a rare and underrecognized morphologic pattern that closely mimics DCIS and poses significant diagnostic challenges. The presence of lymph node metastases with DCIS-like morphology underscores its invasive potential. Accurate recognition requires careful morphological assessment in combination with multiple myoepithelial markers to avoid misdiagnosis and inappropriate clinical management.