Artifactual Displacement of Ductal Carcinoma in Situ (ADDCIS) (Toothpaste Effect): A Mimicker of Invasive Ductal Carcinoma

Needle tract displacement is a recognized mimicker of invasive ductal carcinoma (IDC). Artifactual displacement of ductal carcinoma in situ (ADDCIS) unassociated with needle tracts may occur secondary to mechanical compression of breast specimens but has not been systematically studied. We identified 16 cases of ADDCIS unassociated with needle tract changes; the majority (75%) were internal referrals to the breast pathology service to rule out IDC, 19% were received as external diagnostic consultations to rule out IDC, and 6% were routine second review cases originally diagnosed as IDC at an outside hospital. The majority (62.5%) of ADDCIS occurred in lumpectomies, whereas 25% occurred in mastectomies and 12.5% in core biopsies. ADDCIS foci ranged from <1 to 5 mm; however, all ADDCIS spanning >4 mm demonstrated a linear pattern of displacement. In all cases, ADDCIS involved mammary stroma in a nonlobular distribution; in half, ADDCIS extended between benign lobules. Immunohistochemistry revealed no myoepithelial cells around the ADDCIS (n=7), adding to the concern for IDC. However, in contrast to most IDC, ADDCIS lacked stromal reaction and showed degenerative, smudged chromatin. None of the 9 patients with significant follow-up (mean, 7 y) developed metastasis. All received further local therapy for DCIS (5 radiation, 4 completion mastectomy); 1 received adjuvant systemic therapy (hormone therapy for contralateral IDC). In conclusion, ADDCIS mimics IDC, particularly given its permeative pattern and absence of myoepithelial cells. ADDCIS is most common in lumpectomies but can occur in mastectomies or core biopsies. Diagnostic clues include smudged nuclear chromatin, lack of stromal response, and linear pattern of displacement in larger lesions. The benign follow-up without systemic therapy supports our view that ADDCIS does not represent true IDC.