The term "classic invasive lobular carcinoma" of the breast defines breast malignancies of vastly different nature

PURPOSE

To describe in detail the special features of a previously unappreciated "classic invasive lobular carcinoma" which is confined to the terminal ductal lobular units (TDLUs) and differs considerably from the extensive classic invasive lobular carcinoma, and to suggest specific terminology.

METHOD

All invasive breast cancer cases without associated microcalcifications diagnosed in our Institution with the histopathologic diagnosis of classic invasive lobular carcinoma during the years 1996-2019 (n = 560) formed the basis of this study. The cases were prospectively classified according to their imaging biomarkers (mammographic features) and followed up to Dec 31, 2021, to determine long-term patient outcome. An additional 2600 invasive breast cancer cases (diagnosed other than invasive lobular carcinoma) without associated microcalcifications served as a reference group. Detailed histopathologic analysis used large format (10x8 cm) thin section technique and staining methods including hematoxylin-eosin (H&E), E-cadherin, cytokeratin CK 5/6, a transmembrane glycoprotein (CD44) and anti-actin or anti-smooth muscle myosin heavy chain.

RESULTS

The imaging biomarkers differentiated two separate disease subgroups, having the same histopathologic diagnosis, classic invasive lobular carcinoma. One of these has the imaging biomarker of extensive architectural distortion with no central tumour mass, occupies the extralobular mesenchyme and has a long-term survival of 56%. The other subgroup forms stellate or circular non-calcified tumour masses usually smaller than 20 mm, which appear to arise in the intralobular mesenchyme, and has a significantly better long-term survival of 84%.

CONCLUSIONS

There is a striking difference between the subgross histopathology and the mammographic appearance (imaging biomarkers) of two breast malignancies having the same histopathologic diagnosis, "classic invasive lobular carcinoma". The large difference in the long-term outcome of these two tumour types is even more striking. Using the same specific term, "classic invasive lobular carcinoma", to describe these two separate entities can adversely affect management decisions.

Imaging biomarkers are underutilised but highly predictive prognostic factors for the more fatal breast cancer subtypes

PURPOSE

The development and refinement of breast imaging modalities offer a wealth of diagnostic information such as imaging biomarkers, which are primarily the mammographic appearance of the various breast cancer subtypes. These are readily available preoperatively at the time of diagnosis and can enhance the prognostic value of currently used molecular biomarkers. In this study, we investigated the relative utility of the molecular and imaging biomarkers, both jointly and independently, when predicting long-term patient outcome according to the site of tumour origin.

METHODS

We evaluated the association of imaging biomarkers and conventional molecular biomarkers, (ER, PR, HER-2, Ki67), separately and combined, with long-term patient outcome in all breast cancer cases having complete data on both imaging and molecular biomarkers (n = 2236) diagnosed in our Institute during the period 2008-2019. Large format histopathology technique was used to document intra- and intertumoural heterogeneity and select the appropriate foci for evaluating molecular biomarkers.

RESULTS

The breast cancer imaging biomarkers were strongly predictive of long-term patient outcome. The molecular biomarkers were predictive of outcome only for unifocal acinar adenocarcinoma of the breast (AAB), but less reliable in the multifocal AAB cases due to variability of molecular biomarkers in the individual tumour foci. In breast cancer of mesenchymal origin (BCMO), conventionally termed classic invasive lobular carcinoma, and in cancers originating from the major lactiferous ducts (ductal adenocarcinoma of the breast, DAB), the molecular biomarkers misleadingly indicated favourable prognosis, whereas the imaging biomarkers in BCMO and DAB reliably indicated the high risk of breast cancer death. Among the 2236 breast cancer cases, BCMO and DAB comprised 21% of the breast cancer cases, but accounted for 45% of the breast cancer deaths.

CONCLUSIONS

Integration of imaging biomarkers into the diagnostic workup of breast cancer yields a more precise, comprehensive and prognostically accurate diagnostic report. This is particularly necessary in multifocal AAB cases having intertumoural heterogeneity, in diffuse carcinomas (DAB and BCMO), and in cases with combined DAB and AAB. In such cases, the imaging biomarkers should be prioritised over molecular biomarkers in planning treatment because the latter fail to predict the severity of the disease. In combination with the use of the large section histopathology technique, imaging biomarkers help alleviate some of the current problems in breast cancer management, such as over- and under-assessment of disease extent, which carry the risk of overtreatment and undertreatment.

Multifocal and diffusely infiltrating breast cancers are highly fatal subgroups needing further improvement in diagnostic and therapeutic strategies

Physicians treating breast cancer patients often wonder why this dreaded disease is still fatal in some women despite our best diagnostic and therapeutic efforts. Our own studies on prospectively documented cases spanning several decades have given us new insights for approaching this problem. By using imaging biomarkers to classify breast cancer subtypes according to their apparent site of origin, we found that a majority of breast cancer deaths (71%) occur in a minority of breast cancers (45%). Breast cancer deaths are significantly more likely to occur in women with multifocal acinar adenocarcinoma of the breast, AAB (13.1%), diffusely invasive breast cancers of ductal origin, DAB (24 %) and breast malignancies of mesenchymal hybrid cell origin, BCMO (33.7%) compared with women having unifocal invasive breast cancers (6.1%). Preventing more of these fatal events will require a re-evaluation of the current imperfect histopathologic terminology of breast cancer with special attention to the diffuse breast cancer subtypes, intensification of multimodality imaging and multidisciplinary management, as well as application of image guided large format histopathology.

The challenging imaging and histopathologic features of diffusely infiltrating breast cancer

PURPOSE

Clinical, imaging and outcome observations indicate that diffusely infiltrating breast cancer, presenting as a large region of architectural distortion on the mammogram and conventionally termed classic infiltrating lobular carcinoma of diffuse type, represents a very unusual breast malignancy. This article aims to draw attention to the complex clinical, imaging, and large format thin and thick section histopathologic features of this malignancy, which challenges our current diagnostic and therapeutic management practices.

METHODS

Prospectively collected data from the randomized controlled trial (1977-85) and from the subsequent, ongoing population-based mammography service screening (1985-2019) with more than four decades of follow up in Dalarna County, Sweden provided the database for investigating this breast cancer subtype. Large format thick (subgross) and thin section histopathologic images of breast cancers diagnosed as "diffusely infiltrating lobular carcinoma of the breast" were correlated with their mammographic tumour features (imaging biomarkers) and the long-term patient outcome.

RESULTS

This malignancy does not have a distinct tumour mass or focal skin retraction at clinical breast examination; instead, it causes an indistinct "thickening" and eventually shrinks the entire breast. A dominant feature is extensive architectural distortion on the mammograms caused by an excessive amount of cancer-associated connective tissue. Unlike other invasive breast malignancies, this subtype forms concave contours with the surrounding adipose connective tissue, a feature that makes it difficult to detect on mammograms. Women with this diffusely infiltrating breast malignancy have a 60% long-term survival. Its long-term patient outcome is surprisingly poor compared to that expected from its relatively favourable immunohistochemical biomarkers, including a low proliferation index and remains unaffected by adjuvant therapy.

CONCLUSIONS

The unusual clinical, histopathologic and imaging features of this diffusely infiltrating breast cancer subtype are consistent with a site of origin quite different from that of other breast cancers. Additionally, the immunohistochemical biomarkers are deceptive and unreliable because they indicate a cancer with favourable prognostic features predictive of a good long-term outcome. The low proliferation index is usually indicative of a breast cancer with a good prognosis, but in this subtype the prognosis is poor. If we are to improve the dismal outcome of this malignancy, it will be necessary to clarify its true site of origin, which will be a prerequisite for gaining a better understanding why current management efforts often fail and why the fatality rate is so unfortunately high. Breast radiologists should be watchful for the development of subtle signs of architectural distortion at mammography. Large format histopathologic technique enables adequate correlation of the imaging and histopathologic findings.

Can we improve breast cancer management using an image-guided histopathology workup supported by larger histopathology sections?

PURPOSE

Breast radiologists examine the entire breast in full-size images, while breast pathologists examine small tissue samples at high magnification. The diagnostic information from these complementary imaging approaches can be difficult to integrate for a more clinically relevant evaluation of malignancies spanning several centimetres. We have explored the advantages and disadvantages of imaging guided larger section pathology techniques compared with the standard 2 × 2.5 cm. small section technique.

METHODS

We compared the ability of conventional small section histopathology with larger section histopathology techniques to examine surgical resection margins and full disease extent. We evaluated the pre-surgical imaging workup and use of microfocus magnification radiography of sliced surgical specimens in the histopathologic evaluation of disease extent and status of surgical margins.

RESULTS

Image assisted large section histopathology of excised breast tissue enables comprehensive examination of an approximately tenfold larger contiguous tissue area than is provided by conventional small section technology. Attempting to cover the full area of each consecutive slice of resected tissue is more labour-intensive and expensive with the small section approach and poses challenges in reconstituting three-dimensional tumour architecture after morcellation and sectioning. Restricting histopathologic examination to a limited number of samples provides an incomplete evaluation of surgical margins.

CONCLUSIONS

A considerably improved documentation of breast cancer and a more reliable assessment of tissue margins is provided by using larger sized histopathology samples to correlate with breast imaging findings. These in turn can enable more appropriate treatment planning, improved surgical performance, fewer recurrences, and better patient outcome. Uncertainty of surgical margin evaluation inherent to the standard small section technique can lead to inappropriate decisions in surgical management and adjunctive therapy. Progress in breast diagnosis and treatment will largely depend on whether histopathology terminology and technique will undergo a revolution similar to the one that has already occurred in breast imaging.