Multifocal/multicentric breast cancer: Does each focus matter?

Pathologic Features of Malignancies Presenting as Asymmetry on Mammography

The majority of breast cancers have a solid tumor growth pattern and are seen on mammography as dense masses with defined borders. Cancers detected as asymmetry are rare, and little has been published about their pathologic features. These cancers do not form discrete masses, and a border is not evident. This retrospective case series was undertaken to identify malignancies presenting as asymmetry, to describe their histologic and biologic features and to correlate these features with the mammographic appearance. During the 7.5 years of the study, 18,419 coreneedle biopsies were performed and 42 cases of malignancy presenting as asymmetry were diagnosed (0.2%). The majority were invasive carcinomas (30% or 71%), followed by ductal carcinoma in situ (9% or 21%) and lymphoma (3% or 7%). The invasive carcinomas could be divided into 3 groups: very small unifocal (T1a) carcinomas, larger unifocal carcinomas, and cases with multiple foci of invasion. The latter group had a higher rate of lymph node metastases and more stage III cancers. The invasive carcinomas were predominantly of special histologic types and associated with a minimal stromal response. In contrast, the cases of ductal carcinoma in situ tended to be of higher grade and elicited periductal fibrosis, which likely contributed to the increased density seen on mammography. Although most of the invasive carcinomas were of favorable biologic type (97%) and were stage I (67%), triple-negative carcinomas and stage III carcinomas were also detected. When evaluating core needle biopsies performed for asymmetry, pathologists should be aware that these cancers can have a subtle infiltrative appearance with little or no desmoplastic response, mirroring their appearance by imaging.

Intertumoral heterogeneity of bifocal breast cancer: a morphological and molecular study

PURPOSE

To analyze concordance rates between individual foci of bifocal BC for histological grade, type and intrinsic subtype based on immunohistochemical (IHC) and mRNA-testing using MammaTyper.

METHODS

We evaluated histological grade and type as well as intrinsic subtype based on IHC status for estrogen and progesterone receptors, HER2 and the mitotic activity index in 158 individual foci of 79 bifocal BC. A subgroup of 31 cases additionally underwent mRNA-based subtyping using the MammaTyper (MT) test. We calculated concordance rates between individual foci, as well as Cohen's Kappa (K).

RESULTS

For 79 bifocal BC, concordance rates between individual foci for grade, histological type, and IHC-based subtype were 69.6% (K=0.53), 92.4% (K=0.81), and 74.7% (K=0.62), respectively. In the MT subgroup of 31 bifocal BC, concordance rates between individual foci for grade, histological type, IHC-based and mRNA-based intrinsic subtype were 87.1% (K=0.78), 90.3% (K=0.73), 87.1% (K=0.82), and 87.1% (K=0.7), respectively. Overall concordance between IHC- and mRNA-based subtype in the MT subgroup was 79% (K=0.7). In 6/79 cases (7.6%), testing of the smaller focus added clinically relevant information either on IHC- or mRNA-level: four cases showed high hormonal receptor expression while the expression in the larger focus was negative or low, warranting additional endocrine treatment; two cases presented with higher proliferative activity in the smaller focus, warranting additional chemotherapy.

CONCLUSION

In bifocal BC, intertumoral heterogeneity on the morphological, immunohistochemical and molecular level is common, with discordant intrinsic subtype in up to 25% between individual foci, with about 8% clinically relevant discordances.