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Aims The aims of this study were to review the histological features useful for the identification of metastases to the breast and to investigate the impression that this diagnosis has become more common. Methods and results The histological features of metastases to the breast from 2008 to 2018 were reviewed. Seventy-four biopsies from 66 patients were identified: 1% compared with primary carcinoma of the breast. Non-haematological metastases comprised 0.75% compared with 0.3% in a series from 1996 to 2005. The most common tumour types were pulmonary carcinoma (22), lymphoma (15), melanoma (13), gastrointestinal carcinoma (eight) and serous papillary carcinoma (four). In 73% there were histological features that were not typical of primary mammary carcinoma. Some metastases were histologically similar to breast cancer and the history was essential to making the correct diagnosis. Useful histological clues included small-cell morphology for pulmonary carcinoma, glands containing necrosis for gastrointestinal carcinoma, intranuclear inclusions, marked pleomorphism and spindle cells for melanoma, clear cells for renal carcinoma, papillary architecture for serous papillary carcinoma and sheets of centroblasts or nodules of centroblasts and centrocytes for lymphoma. Useful immunohistochemical markers included TTF-1 for pulmonary carcinoma, S100, melan-A and HMB45 for melanoma, CK20 and CDX2 for colorectal carcinoma, PAX8 and WT1 for serous papillary carcinoma and lymphoid markers for lymphomas, in addition to the absence of expression of mammary markers ER, GATA3 and GCDFP-15. Conclusion The majority of metastases to the breast have histological clues to the diagnosis. Immunohistochemistry is helpful. This diagnosis is being made more frequently.

Background: Phyllodes tumours (PT) are rare and distinct breast tumours, which span a morphological continuum. Classification into benign, borderline and malignant categories reflects their biology and clinical behaviour and is essential to guide management. This study aims to assess the diagnostic agreement of PT using the UK National Health Service Breast Screening Programme (NHSBSP) breast pathology external quality assurance (EQA) scheme data. Methods: 26 PTs were identified in the EQA scheme, which were diagnosed by an average of 607 participants/circulation. Data on diagnostic categories were collected, and representative slides were reviewed. The level of concordance between reporting pathologists was assessed. Results: There were 14 benign, 6 borderline and 6 malignant PT. The overall rate of diagnosis agreement was 86% when analysed as benign lesions, borderline PT and malignant lesions, which decreased to 79% when diagnosed as PT (irrespective of grade) and to 63% when the diagnosis was further refined to PT categories (benign, borderline and malignant PTs). The highest agreement rate was observed in malignant PT (86%) and the lowest in borderline PT (42%). Malignant heterologous elements, stromal overgrowth and leaf-like architecture are features associated with higher concordance rates. Lower priority features were stromal expansion, clefting, and multinodularity. Conclusion: The concordance of PT diagnosis, as an entity, is high, but its classification into benign, borderline and malignant has variable agreement levels, with borderline tumours having the lowest concordance rate. More research to refine the diagnostic criteria for categorisation of PT is warranted to improve concordance between pathologists.

AimsThe clinical significance of radial scar (RS)/complex sclerosing lesion (CSL) with high-risk lesions (epithelial atypia) diagnosed on needle core biopsy is not well defined. We aimed at assessing the upgrade rate to ductal carcinoma in situ (DCIS) and invasive carcinoma on the surgical excision specimen in a large cohort with RS/CSL associated with atypia.Methods157 women with a needle core biopsy diagnosis of a RS/CSL with atypia and follow-up histology were studied. Histological findings, including different forms of the atypical lesions and final histological outcome in the excision specimens, were retrieved and analysed, and the upgrade rates for malignancy and for invasive carcinoma were calculated.Results69.43% of the cases were associated with atypical ductal hyperplasia (ADH) or atypia not otherwise classifiable, whereas lobular neoplasia was seen in 21.66%. On final histology, 39 cases were malignant (overall upgrade rate of 24.84%); 12 were invasive and 27 had DCIS. The upgrade differed according to the type of atypia and was highest for ADH (35%). When associated with lobular neoplasia, the upgrade rate was 11.76%. The upgrade rate’s variability was also considerably lower when considering the upgrade to invasive carcinoma alone for any associated lesion.ConclusionsThe upgrade rate for ADH diagnosed on needle core biopsy with RS is similar to that of ADH without RS and therefore should be managed similarly. RS associated with lobular neoplasia is less frequently associated with malignant outcome. Most lesions exhibiting some degree of atypia showed a similar upgrade rate to invasive carcinoma. Management of RS should be based on the concurrent atypical lesion.

Encapsulated and solid papillary carcinomas (EPCs and SPCs) are considered historically as a special form of ductal carcinoma in situ. Invasive lobular carcinoma (ILC) is characterised by a discohesive growth pattern. There are several variants of ILC, but, as yet, no papillary subtype has been identified. Here we report 3 cases of ILC presenting as papillary carcinoma (PC) with a typical solid papillary growth pattern. One case was reported on core biopsy as EPC (B5a). The 3 ensuing resection specimens showed features typical of SPC with a circumscribed malignant epithelial proliferation containing fibrovascular cores and surrounded, at least focally, by a thick fibrous capsule. The lobular nature of these tumours was confirmed on the resection specimens by the absence of E-cadherin and β-catenin membrane expression. The invasive nature was confirmed by the presence of entrapped fat cells, the absence of myoepithelial cells and focal merging of the solid papillary areas with classic ILC at the periphery. Of note, 1 case was a recurrent carcinoma without an in situ component. Conclusion: This study provides further evidence that EPC and SPC represent a unique growth pattern of breast carcinomas rather than reflecting the in situ or invasive nature of the tumour, and that ILC can acquire a papillary growth pattern.

AimsThis study aims to assess the diagnostic agreement of lymphovascular invasion (LVI) in invasive breast cancer (BC).MethodsData on LVI were collected from the UK National Health Service Breast Screening Programme pathology external quality assurance scheme database. 101 BCs assessed over a 10-year period (2004–2014) were included. Cases were scored by an average of 600 pathologists. Three H&E stained slides from each case were reviewed by three pathologists and additional variables were evaluated.ResultsIn the whole series, the overall κ value was 0.4 (range 0.26–0.53). On review, LVI was detected in all three slides in 20 cases (20%), in two slides in 12 cases and in one of the three slides in 9 cases and was not seen in 60 cases. For concordance analysis, the first and last groups were used to represent cases with definite (LVI+) and absent LVI (LVI–), respectively. In the LVI+group (n=20), the level of agreement ranged from 0.54 to 0.99 (median 0.86). In the LVI– group (n=60), the level of agreement ranged from 0.52 to 1.00 (median 0.93), with 44% of cases showing interobserver concordance of >95%. There was a correlation between increasing number of involved lymphovascular spaces in the section and higher LVI reporting concordance. Some degree of retraction/fixation artefacts was observed in 35% of cases; this was associated with a lower concordance rate.ConclusionsThe concordance of reporting LVI is variable. Cases without LVI and those with multiple involved vessels are likely to have the highest concordance and the highest detection rates.