Quantitative comparison of immunohistochemical HER2-low detection in an interlaboratory study.

AIMS: Recently, human epidermal growth factor 2 (HER2)-low (i.e. HER2 score 1+ or 2+ without amplification) breast cancer patients became eligible for trastuzumab-deruxtecan treatment. To improve assay standardisation and detection of HER2-low in a quantitative manner, we conducted an external quality assessment-like study in the Netherlands. Dynamic range cell lines and immunohistochemistry (IHC) calibrators were used to quantify HER2 expression and to assess interlaboratory variability. METHODS AND RESULTS: Three blank slides with a dynamic range cell line and an IHC calibrator were stained with routine HER2 assays by 35 laboratories. Four different antibody clones were used: 19 (54.3%) 4B5, six (17.1%) A0485, five (14.3%) DG44 (HercepTest) and five (14.3%) SP3. Laboratories used two different detection kits for 4B5 assays: 14 (73.7%) ultraView and five (26.3%) OptiView. Variability of HER2 expression in cell lines, measured with artificial intelligence software, was median (min-max) = negative core 0.5% (0.0-57.0), 1+ core 4.3% (1.6-71.3), 2+ core 42.8% (30.4-92.6) and 3+ core 96.2% (91.8-98.8). The calibrators DG44 and 4B5 OptiView had the highest analytical sensitivity, closely followed by 4B5 ultraView. SP3 was the least sensitive. Calibrators of A0485 assays were not analysable due to background staining. CONCLUSIONS: As assays were validated for detecting HER2-amplified tumours, not all assays and antibodies proved suitable for HER2-low detection. Some tests showed distinct expression in the negative cell line. Dynamic range cell line controls and quantitative analysis using calibrators demonstrated more interlaboratory variability than commonly appreciated. Revalidation of HER2 tests by laboratories is needed to ensure clinical applicable HER2-low assays.

Novel markers in breast pathology.

Breast pathology is an ever-expanding database of information which includes markers, or biomarkers, that detect or help treat the disease as prognostic or predictive information. This review focuses on these aspects of biomarkers which are grounded in immunohistochemistry, liquid biopsies and next-generation sequencing.

Avoiding "False Positive" and "False Negative" Immunohistochemical Results in Breast Pathology.

Immunohistochemistry (IHC) plays an important role in the evaluation of breast pathology specimens to provide both diagnostic and prognostic/therapeutic information. Although most IHCs used in breast pathology can be easily interpreted, pitfalls do exist, especially in some uncommon scenarios. This review intends to focus on the challenging areas such as the interpretation of myoepithelial cell markers in differentiating benign proliferation and in situ carcinoma from invasive carcinoma, lobular cell markers in differentiating lobular from ductal carcinoma, cytokeratin and other markers in diagnosing metaplastic carcinoma, and breast tissue origin markers in diagnosing breast primary carcinoma. The challenges in interpreting prognostic and predictive markers will be also discussed.

Prosigna® breast cancer assay: histopathologic correlation, development, and assessment of size, nodal status, Ki-67 (SiNK™) index for breast cancer prognosis.

The Prosigna® assay is a United States Food and Drug Administration (US-FDA) cleared molecular test for prognostic use in hormone receptor-positive stage I/II breast cancer in postmenopausal women. We analyzed histopathologic features of 79 cases with Prosigna® assay results and found a significant correlation between tumor size, grade, and Ki-67 labeling index with Prosigna® score (0-40, 41-60, and 61-100) and Prosigna® risk categories. Since the Prosigna® risk stratification is influenced by lymph node status, we designed an index that included lymph node status and the two most correlated variables (size and Ki-67 labeling index). This was termed the size, nodal, and Ki-67 (SiNK™) index and is calculated as follows: (size in mm) + (pN × 10) + (Ki-67 labeling index). The SiNK™ index was divided into ≤40 and >40 to test its prognostic significance in a well-characterized dataset of 106 ER+/HER2-negative stage I-II invasive breast cancers treated with standard multi-modality therapy with long term follow-up (average 101 months follow-up). Patients with SiNK™ ≤40 showed significantly improved distant recurrence-free survival (96% distant recurrence-free survival in SiNK™ ≤40 compared to 81% in SiNK™ >40; log-rank test p value: 0.0027). SiNK™ provides strong prognostic information in ERo+/HER2-negative breast cancers. SiNK™ index is simple to calculate using data from routine pathology reports. This should be further evaluated in larger datasets.

Magee Equations™ and response to neoadjuvant chemotherapy in ER+/HER2-negative breast cancer: a multi-institutional study.

Magee Equations™ (ME) are multivariable models that can estimate oncotype DX® recurrence score. One of the equations, Magee Equation 3 (ME3) which utilizes only semi-quantitative receptor results has been shown to provide chemopredictive value in the neoadjuvant setting in a single institutional study. This multi-institutional study (seven institutions contributed cases) was undertaken to examine the validity of ME3 in predicting response to neoadjuvant chemotherapy in estrogen receptor positive, HER2-negative breast cancers. Stage IV cases were excluded. The primary endpoint was the pathologic complete response (pCR) rate in different categories of ME3 scores calculated based on receptor results in the pre-therapy core biopsy. A total of 166 cases met the inclusion criteria. The patient age ranged from 24 to 83 years (median 53 years). The average pre-therapy tumor size was 3.9 cm, and axillary lymph nodes were confirmed positive by pre-therapy core biopsy in 85 of 166 cases (51%). The pCR rate according to ME3 scores was 0% (0 of 64) in ME3 < 18, 0% (0 of 46) in ME3 18-25, 14% (3 of 21) in ME3 > 25 to <31, and 40% (14 of 35) in ME3 score 31 or higher (p value: <0.0001). There were no distant recurrences and no deaths in the 17 patients with pCR. In the remaining 149 cases with residual disease, ME3 score of >25 was significantly associated with shorter distant recurrence-free survival and showed a trend for shorter breast cancer-specific survival. The results of this multi-institutional study are similar to previously published data from a single institution (PMID: 28548119) and confirm the chemo-predictive value of ME3 in the neoadjuvant setting. In addition, ME3 may provide prognostic information in patients with residual disease which should be further evaluated.

Metaplastic carcinomas of the breast without evidence of epithelial differentiation: a diagnostic approach for management.

AIMS: Although rare, malignant sarcomatoid breast tumours without evidence of epithelial differentiation comprise a diagnostic challenge with management implications. Earlier studies have generally considered these to be primary breast sarcomas; however, supporting evidence is lacking and management remains variable. This study aimed to provide an evidence-based approach to improve the consistency of diagnosis and management for such cases. METHODS AND RESULTS: A large series (n = 140) of metaplastic breast carcinoma (MBC) diagnosed in Nottingham over 18 years was analysed. Only cases with available data on immunohistochemical expression of cytokeratins (CKs) were included. The prevalence and pattern of expression for various CKs were assessed and details of tumours negative for CKs were collected. A diagnostic approach based on our experience is provided. Forty-seven cases (34%) showed foci of conventional type invasive breast carcinoma or ductal carcinoma in situ (DCIS), while 93 cases (66%) were diagnosed as MBC based on morphology and/or CK expression. Ninety-seven cases (69%) were negative for one or more CKs, with 18 cases (13%) negative for five or more CKs. Eight cases (6%) lacked expression of all CKs tested. Further examination showed evidence of carcinomatous nature in five cases, and three were diagnosed as MBC following extensive diagnostic work-up and based on our experience. CONCLUSION: This study suggests that MBC represents a spectrum of neoplasms, with some lacking CK expression. Sarcomatoid neoplasms of the breast lacking evidence of carcinomatous morphology and CK expression may represent an extreme end of differentiation that can be considered as carcinomas rather than sarcomas for management purposes (following extensive work-up).

Immunohistochemical Markers With Potential Diagnostic, Prognostic, and Therapeutic Significance in Uterine Carcinosarcoma: A Clinicopathologic Study of 43 Cases.

Uterine carcinosarcomas (UCS) are rare and highly aggressive tumors. Although it is currently accepted that the majority of UCS are metaplastic carcinomas, their aggressive behavior is unparalleled to that of any other high-grade endometrial neoplasms. Therefore, the search for the distinct immunohistochemical and molecular features that could help in the development of new treatment strategies continues. We evaluated the expression of PDL-1, growth hormone releasing hormone receptor, p53, WT1, PAX-8, estrogen receptor, HNF-1, and mismatch repair proteins in 43 UCS. Tumors were selected from the archives of the Magee-Womens Hospital University of Pittsburgh Medical Center Department of Pathology. Seventeen were stage I, 4 were stage II, 15 were stage III, and 7 were stage IV. The median age was 67 yr and median overall survival was 3.2 yr. Immunostaining for PAX8, HNF-1, and estrogen receptor showed statistically significant difference between epithelial and stromal components. Expression of p53 was significantly associated with clinical high stage, but other markers did not correlate with stage or survival. Immunostaining for programmed death ligand-1 was strongly positive in 30 UCS (70%), including 24 cases with tumor cell positivity, 12 cases with tumor cell and tumor-infiltrating immune cell positivity, and 6 cases with tumor-infiltrating immune cell positivity only. Of 27 tumors tested for mismatch repair expression, 12 (44%) showed loss of expression, 7 of which were PDL-1 positive. Growth hormone releasing hormone receptor was positive in 38 tumors (88%) and predominantly expressed in the epithelial component. The range of positivity for programmed death ligand-1 and growth hormone releasing hormone receptor suggests a possible potential adjuvant treatment that may be considered for UCS.

The healthcare value of the Magee Decision Algorithm™: use of Magee Equations™ and mitosis score to safely forgo molecular testing in breast cancer.

Magee Equations™ are multivariable models that can estimate oncotype DX® Recurrence Score, and Magee Equation 3 has been shown to have chemopredictive value in the neoadjuvant setting as a standalone test. The current study tests the accuracy of Magee Decision Algorithm™ using a large in-house database. According to the algorithm, if all Magee Equation scores are <18, or 18-25 with a mitosis score of 1, then oncotype testing is not required as the actual oncotype recurrence score is expected to be ≤25 (labeled "do not send"). If all Magee Equation scores are 31 or higher, then also oncotype testing is not required as the actual score is expected to be >25 (also "do not send"). All other cases could be considered for testing (labeled "send"). Of the 2196 ER+, HER2-negative cases sent for oncotype testing, 1538 (70%) were classified as "do not send" and 658 (30%) as "send". The classification accuracy in the "do not send" group was 95.1%. Of the 75 (4.9%) discordant cases (expected score ≤25 by decision algorithm but the actual oncotype score >25), 26 received endocrine therapy alone. None of these 26 patients experienced distant recurrence (average follow-up of 73 months). The Magee Decision Algorithm accurately identifies cases that will not benefit from oncotype testing. Such cases constitute ~70% of the routine clinical oncotype requests, an estimated saving of $300,000 per 100 test requests. The occasional discordant cases (expected ≤25, but actual oncotype score >25) appears to have an excellent outcome on endocrine therapy alone.

Breast cancer global tumor biomarkers: a quality assurance study of intratumoral heterogeneity.

Biomarker analysis of invasive breast carcinoma is useful for prognosis, as surrogate for molecular subtypes of breast cancer, and prediction of response to adjuvant and neoadjuvant systemic therapies. Breast cancer intratumoral heterogeneity is incompletely studied. Comprehensive biomarker analysis of estrogen receptor (ER), progesterone receptor (PR), HER2, and Ki67 labeling index was performed on each tissue block of 100 entirely submitted breast tumors in 99 patients. Invasive carcinoma and in situ carcinoma was scored using semiquantitative histologic score (H-score) for ER and PR, HER2 expression from 0 to 3+, and percentage positive cells for Ki67. Core biopsy results were compared with surgical excision results, invasive carcinoma was compared with in situ carcinoma, and interblock tumoral heterogeneity was assessed using measures of dispersion (coefficient of variation and quartile coefficient of dispersion). Overall concordance between core biopsy and surgical excision was 99% for ER and 95% for PR. Mean histologic score of ER was significantly lower in invasive carcinoma between core biopsy and surgical excision (p = 0.000796). Intratumoral heterogeneity was higher for PR than for ER (mean coefficient of variation for ER 0.08 stdv 0.13 vs. PR 0.26 stdv 0.41). Ki67 labeling index was significantly higher in invasive carcinoma as compared with associated ductal carcinoma in situ on surgical resection specimen (p ≤ 0.0001). Ki67 hotspots were identified in 47% of cases. Of 52 HER2 negative cases on core biopsy, 10 were scored as equivocal on surgical resection. None (0/10) were amplified by Her-2/neu fluorescence in situ hybridization. Overall, biomarkers on core biopsy showed concordance with the surgical excision specimen in the vast majority of cases. Biomarker expression of in situ closely approximates associated invasive carcinoma. Intratumoral heterogeneity of PR is greater than ER. Biomarker expression on diagnostic core biopsy or single tumor block is representative of breast carcinoma as a whole in most cases and is appropriate for clinical decision-making.

Metaplastic breast carcinoma: a clinical-pathologic study of 97 cases with subset analysis of response to neoadjuvant chemotherapy.

Metaplastic breast carcinoma is a rare heterogeneous category of breast cancer, often associated with a poor prognosis. Clinical-pathologic studies with respect to varied morphologic subtypes are lacking. There is also a dearth of studies assessing the response of metaplastic breast carcinoma to neoadjuvant chemotherapy. Cases of metaplastic breast carcinoma diagnosed between 2007 and 2017 were identified. Various clinical-pathologic variables were tested for association with survival. Patients who underwent neoadjuvant chemotherapy were assessed for pathologic response. Median age at diagnosis with metaplastic breast carcinoma was 64 years. With a median follow-up of 39 months, 26 patients (27%) recurred (24 distant and 2 loco-regional). The overall survival rate of the cohort was 66% (64/97). A number of variables were associated with survival in univariable analysis; however, in multivariable analysis, only lymph node status and tumor size (pT3 vs. pT1/2) were significantly associated with all survival endpoints: recurrence-free survival, distant recurrence-free survival, overall survival and breast cancer-specific survival. Twenty-nine of 97 (30%) patients with metaplastic breast carcinoma received neoadjuvant chemotherapy. Five (17%) patients achieved pathologic complete response. Matrix-producing morphology was associated with higher probability of achieving pathologic complete response (p = 0.027). Similar to other breast cancer subtypes, tumor size and lymph node status are prognostic in metaplastic carcinomas. The pathologic complete response rate of metaplastic breast carcinoma in our cohort was 17%, higher than previously reported. Although the matrix-producing subtype was associated with pathologic complete response, there was no survival difference with respect to tumor subtypes.

Follow-up outcomes of benign vascular lesions of breast diagnosed on core needle biopsy: A study of 117 cases.

Benign vascular lesions of breast are uncommon findings on core biopsy and surgical excision has been recommended to rule out a more serious lesion. However, a recent study suggested that excision may be spared for vascular lesion without atypia. The aim of this study was to assess the follow-up outcomes in lesions yielding benign vascular lesions on core biopsy. We retrospectively reviewed 117 patients with diagnosis of hemangioma (106 patients) and atypical hemangioma (11 patients) on core biopsy at our institution over an 18-year period. Majority of benign vascular lesions were followed-up clinically and/or radiologically. Surgical excision was performed on 18 patients (16.9%) with benign hemangiomas and all 11 patients (100%) with atypical hemangiomas. Upon excision, the majority of patients (82.8%, 24/29) retained benign final pathology and five patients (17.2%) were atypical hemangioma. There was no upgrade on excision. All patients had a benign course regardless whether the lesions were excised or not. Our findings support the recent study that benign vascular lesion of breast may not require surgical excision.

Pathologist's health-care value in the triage of Oncotype DX® testing: a value-based pathology study of tumour biology with outcomes.

AIMS: Pathologists provide expert tissue assessment of breast cancer, yet their value to guide the appropriate use of breast cancer gene expression profile tests (GEPT) is underutilised. The specific aims of this study are to report morpho-immunohistological characteristics of breast tumours with Oncotype DX® (ODx) recurrence scores (RS) of 10 or fewer (ultra-low risk) and 25 or fewer (low risk) in order to determine if pathologists can identify prospectively patient tumours that do not require ODx testing. METHODS AND RESULTS: Oncotype DX® cases with RS < 10 from 2005 to 2010 comprised 441 of 2594 (17%) of clinical cases; this cohort had 5 years' follow-up and was treated with endocrine therapy alone. Tumours were analysed for tumour type, Nottingham grade, mitosis score (MS) semi-quantitative (H-score) hormone receptor content and Magee equation 3. Knowledge derived from this data set was used to develop algorithms in order to identify prospectively tumours with RS of 10 or fewer or 25 or fewer. Thirty-four per cent of tumours were low-grade special types, while the remainder were enriched with high hormone receptor content with MS of 1. These algorithmic selection criteria identified correctly all patient cases below the chemotherapy cut-point, i.e. RS < 25, indicating that these oncotype test orders were an unnecessary cost. CONCLUSIONS: This unique study demonstrates that (i) pathologists add great value to triage breast cancer for GEPT; and (ii) can identify prospectively low-grade tumour biology with high sensitivity and high specificity for those cases which do not require chemotherapy (RS < 25) using MS and hormone receptor content.

Invasion in breast lesions: the role of the epithelial-stroma barrier.

Despite the significant biological, behavioural and management differences between ductal carcinoma in situ (DCIS) and invasive carcinoma of the breast, they share many morphological and molecular similarities. Differentiation of these two different lesions in breast pathological diagnosis is based typically on the presence of an intact barrier between the malignant epithelial cells and stroma; namely, the myoepithelial cell (MEC) layer and surrounding basement membrane (BM). Despite being robust diagnostic criteria, the identification of MECs and BM to differentiate in-situ from invasive carcinoma is not always straightforward. The MEC layer around DCIS may be interrupted and/or show an altered immunoprofile. MECs may be absent in some benign locally infiltrative lesions such as microglandular adenosis and infiltrating epitheliosis, and occasionally in non-infiltrative conditions such as apocrine lesions, and in these contexts this does not denote malignancy or invasive disease with metastatic potential. MECs may also be absent around some malignant lesions such as some forms of papillary carcinoma, yet these behave in an indolent fashion akin to some DCIS. In Paget's disease, malignant mammary epithelial cells extend anteriorly from the ducts to infiltrate the epidermis of the nipple but do not typically infiltrate through the BM into the dermis. Conversely, BM-like material can be seen around invasive carcinoma cells and around metastatic tumour cell deposits. Here, we review the role of MECs and BM in breast pathology and highlight potential clinical implications. We advise caution in interpretation of MEC features in breast pathology and mindfulness of the substantive evidence base in the literature associated with behaviour and clinical outcome of lesions classified as benign on conventional morphological examination before changing classification to an invasive lesion on the sole basis of MEC characteristics.

Cervical Carcinoma With Divergent Neuroendocrine and Gastrointestinal Differentiation.

Neuroendocrine carcinomas of the uterine cervix are rare tumors with aggressive behavior. They comprise <4% of cervical carcinomas. They may coexist with both adenocarcinoma and squamous cell carcinoma of cervix. Signet ring carcinoma of cervix is a rarer entity and less than 20 cases have been described in the literature. We present a case of a 34-year-old female who presented with systemic thrombosis, splenic mass and a cervical mass which on biopsy showed divergent differentiation of primitive large cell neuroendocrine carcinoma with signet ring cells. The cervical tumor was positive for human papilloma virus 16/18 by in situ hybridization, confirming cervical origin of the tumor. This unusual presentation and morphology needs to be recognized and appropriately evaluated when patients present with tumors of unknown origin in metastatic sites.

Magee Equation 3 predicts pathologic response to neoadjuvant systemic chemotherapy in estrogen receptor positive, HER2 negative/equivocal breast tumors.

Magee Equations were derived as an inexpensive, rapid alternative to Oncotype DX. The Magee Equation 3 utilizes immunohistochemical and FISH data for estrogen receptor (ER), progesterone receptor (PR), HER2 and Ki-67 for its calculation (24.30812+ERIHC × (-0.02177)+PRIHC × (-0.02884)+(0 for HER2 negative, 1.46495 for equivocal, 12.75525 for HER2 positive)+Ki-67 × 0.18649). We hypothesize that Magee Equation 3 scores from pre-therapy core biopsy can predict response to neoadjuvant systemic chemotherapy. A prospectively-maintained database of patients who received neoadjuvant systemic therapy from 2010 to 2014 at a single institution was retrospectively reviewed. Pathologic complete response was defined as absence of invasive tumor in the breast and regional lymph nodes. Of the 614 cases, tumors with missing immunohistochemical results and those that were ER negative or HER2 positive were excluded. This resulted in 237 ER positive, HER2 negative/equivocal tumors that formed the basis of this study. Magee Equation 3 scores were divided into 3 categories similar to Oncotype DX, ie, 0 to <18 (low), 18 to <31 (intermediate), and 31 or higher (high) scores. The pathologic complete response rate for low, intermediate and high Magee Equation 3 scores was 0%, 4%, and 36%, respectively. Patients with high Magee Equation 3 scores were 13 times more likely to achieve pathologic complete response compared to those with Magee Equation 3 scores less than 31 (95% CI 5.09-32.87, P<0.0001). For patients that did not achieve pathologic complete response, high Magee Equation 3 correlated with higher recurrence rate, with the majority occurring in patients with positive lymph nodes in the resection specimen. Magee Equation 3 score ≥31 predicts pathologic complete response in the neoadjuvant setting and for tumor recurrence, when pathologic complete response is not achieved. These results show the utility of Magee Equation 3 in predicting patients who will benefit from chemotherapy but warrant prospective multi-institutional validation.

Biomarker assessment and molecular testing for prognostication in breast cancer.

Current treatment of breast cancer incorporates clinical, pathological and molecular data. Oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) define prognosis and identify tumours for targeted therapy, and remain the sole established single-molecule biomarkers defining the minimum breast cancer pathology data set. Ki67 remains one of the most promising yet controversial biomarkers in breast cancer, implemented routinely in some, but not all, pathology departments. Beyond the single-molecule biomarkers, a host of multigene expression tests have been developed to interrogate the driver pathways and biology of individual breast cancers to predict clinical outcome more accurately. A minority of these assays have entered into clinical practice. This review focuses on the established biomarkers of ER, PR and HER2, the controversial but clinically implemented biomarker Ki67 and the currently marketed gene expression signatures.

Breast lesions of uncertain malignant nature and limited metastatic potential: proposals to improve their recognition and clinical management.

Breast lesions comprise a family of heterogeneous entities with variable patterns of presentation, morphology and clinical behaviour. The majority of breast lesions are classified traditionally into benign and malignant conditions and their behaviour can, in the vast majority of cases, be predicted with a reasonable degree of accuracy. However, there remain lesions which show borderline features and lie in a grey zone between benign and malignant, as their behaviour cannot be predicted reliably. Defined pathological categorization of such lesions is challenging, and for some entities is recognized to be subjective and include a range of diagnoses, and forms of terminology, which may trigger over- or undertreatment. The rarity of these lesions makes the acquisition of clinical evidence problematic and limits the development of a sufficient evidence base to support informed decision-making by clinicians and patients. Emerging molecular evidence is providing a greater understanding of the biology of these lesions, but this may or may not be reflected in their clinical behaviour. Herein we discuss some breast lesions that are associated with uncertainty regarding classification and behaviour, and hence management. These include biologically invasive malignant lesions associated with uncertain metastatic potential, such as low-grade adenosquamous carcinoma, low-grade fibromatosis-like spindle cell carcinoma and encapsulated papillary carcinoma. Other lesions of uncertain malignant nature remain, such as mammary cylindroma, atypical microglandular adenosis, mammary pleomorphic adenoma and infiltrating epitheliosis. The concept of categories of (1) breast lesions of uncertain malignant nature and (2) breast lesions of limited metastatic potential are proposed with details of which histological entities could be included in each category, and their management implications are discussed.

Phyllodes tumours of the breast: a consensus review.

Phyllodes tumours constitute an uncommon but complex group of mammary fibroepithelial lesions. Accurate and reproducible grading of these tumours has long been challenging, owing to the need to assess multiple stratified histological parameters, which may be weighted differently by individual pathologists. Distinction of benign phyllodes tumours from cellular fibroadenomas is fraught with difficulty, due to overlapping microscopic features. Similarly, separation of the malignant phyllodes tumour from spindle cell metaplastic carcinoma and primary breast sarcoma can be problematic. Phyllodes tumours are treated by surgical excision. However, there is no consensus on the definition of an appropriate surgical margin to ensure completeness of excision and reduction of recurrence risk. Interpretive subjectivity, overlapping histological diagnostic criteria, suboptimal correlation between histological classification and clinical behaviour and the lack of robust molecular predictors of outcome make further investigation of the pathogenesis of these fascinating tumours a matter of active research. This review consolidates the current understanding of their pathobiology and clinical behaviour, and includes proposals for a rational approach to the classification and management of phyllodes tumours.