Molecular classification of breast carcinoma in situ

Abstract

Pleomorphic variant of invasive lobular carcinoma (PILC) is an aggressive variant of invasive lobular carcinoma (ILC). Its in situ counterpart, pleomorphic lobular carcinoma in situ (PLCIS) is a recently described entity. Morphologically it has the typical architectural pattern of LCIS, but the neoplastic cells resemble intermediate grade DCIS. Molecular signatures that distinguish PLCIS from DCIS and LCIS would provide additional tools to aid in the histopathologic classification of PLCIS as a lesion distinct from LCIS and DCIS. CIS lesions, obtained from a study cohort of 38 breast cancer patients, were divided into 18 DCIS, 14 PLCIS and 6 LCIS. DNA from microdissected archival tissue was interrogated for loss or gain of 112 breast-cancer-specific genes using the Multiplex Ligation-dependent Probe Amplification Assay (MLPA). Classification Regression Tree (CART) analysis was employed to develop a gene-based molecular classification to distinguish or separate out PLCIS from DCIS and LCIS. Molecular classification via CART, based on gene copy number, agreed with histopathology in 34/38 CIS cases. Loss of CASP1 was predictive of LCIS (n=4) with one misclassified PLCIS. Gain of RELA predicted only the LCIS classification (n=2 cases). STK15 and TNFRSF1B were predictive only for DCIS with no misclassifications. Gain of EHF and TNFRSF1B and loss of NCOA3 were predictive of PLCIS, but not without misclassification. Molecular reclassification by CART was accomplished in 4 CIS cases: 1 PLCIS was reclassified as LCIS, 1 LCIS reclassified as PLCIS, and 2 DCIS cases as PLCIS. This study provides additional rationale for molecular modeling strategies in the evaluation of CIS lesions. This diagnostic aid may serve to minimize misclassification between PLCIS and DCIS, and PLCIS and LCIS, aiding to increase accuracy in the differential diagnosis of CIS lesions.

Fig. (1)

Most breast carcinomas in situ are easily categorized as ductal (DCIS) or lobular (LCIS)

Fig. (2)

Some carcinoma in situ lesions have indeterminate (ID) histological features.

Fig. (3)

Morphologically PLCIS has a typical architectural pattern of LCIS but the neoplastic cells resemble intermediate grade DCIS (DCIS IG).

Fig. (4)

PLCIS is expected to be more aggressive than LCIS.

Fig. (5)

E-cadherin (EC) expression provides some degree of lesion sub typing. A: H & E; B: EC stain.

Fig. (6)

Limitations to EC staining: A negative EC stain cannot unequivocally distinguish DCIS ID from PLCIS.

Fig. (7)

Multiplex Ligation-dependent Probe Amplification (MLPA).

Fig. (8)

The optimal tree sequence with the least error rate yielded 7 terminal nodes (A) with the smallest error rate (B).

Fig. (9)

Regression tree for CIS. The splitting criterion for each node is given within the blue boxes. Terminal nodes (red boxes) indicate class prediction based on gene copy number. The tree generated is initiated as a root node (Node 1) containing all 38 CIS cases. This node is split based on the value of a gene’s copy number obtained from the list of genes determined on a univariate analysis (Table 2).