Phyllodes Tumours of the Breast ~ Classification & Grading

Phyllodes tumours of the breast ~ classification & grading

Dr Puay Hoon Tan Division of Pathology Singapore General Hospital Classification

• Process of categorization, typing or grouping of diseases based on criteria. • Taxonomy ~ science of classification.

2 2 Grading

• With reference to neoplasia & tumours ~ – Grade is a measure of degree of differentiation. – Assessed on histology: • Nuclear pleomorphism • Mitotic activity • Resemblance to normal structures – Usually correlates with clinical behaviour.

3 3 Phyllodes tumour

• Uncommon fibroepithelial neoplasm with proliferation of both epithelial and stromal components. • “Phyllodes” - Derived from the Greek word “phyllon” meaning leaf, and “eidos” meaning form. Acropolis, ἀκρόπολις

φύλλο εἶδο

4 Large tumour stretching skin

Circumscribed bulging mass, mucoid, fleshy, whorled Mastectomy

Excision biopsy Ultrasound scan Phyllodes tumour: fibroepithelial neoplasm resembling intracanalicular fibroadenoma, but with exaggerated fronded pattern and stromal hypercellularity

 0.3-1% of all primary breast tumours.  Affects mature women (40-50 years).  Higher incidence in Asians.  Graded according to histological characteristics.  Tendency to recur if incompletely excised. Benign phyllodes tumour Classification & grading of breast phyllodes tumours

• Classification challenges ~ – Cellular fibroadenoma vs phyllodes tumour. – Metaplastic carcinoma vs malignant phyllodes tumour vs sarcoma. • Grading challenges ~ – Benign, borderline and malignant phyllodes tumours. – Predicting clinical behaviour.

Terms classification & grading are often used interchangeably when applied to breast phyllodes tumours

8 8 Scope

• Historical classification. • Core biopsy diagnosis. • Grading & prediction of biological behaviour. • Overcoming classification challenges ~ . Cellular fibroadenoma vs phyllodes tumour. . Metaplastic carcinoma vs malignant phyllodes tumour vs sarcoma. • Role of molecular data in grading & classification.

9 Breast phyllodes tumours

Historical classification

10 Historical perspectives Cystosarcoma Tumour 1824 phyllodes phyllodes Chelius singled out a ‘cystic hydatid’ of Johannes Müller (Lomonaco, Tumori) the mammary gland 1838 1960

1774 1829 1839-1930 Ochme described a Cooper termed it Numerous terms and 1941 ‘cellular hydatid’, descriptions devoted to rapidly benign growing Owens & Adams - term described tumours the same tumour, eg tumour (about 4kg) of cystosarcoma should be later deemed as intracanalicular a young woman avoided as the lesion is phyllodes fibroma, usually not sarcomatous. pseudosarcoma, Proposed ‘giant serocystic tumour etc. intracanalicular Virchow,1867, opined its fibroadenoma of the breast’ ‘limited malignancy, but capacity to metastasize’ Fiks A. Cystosarcoma Phyllodes of the Mammary Gland – Müller’s Tumour: For the 108th Birthday of Johannes Müller. Virchows Archiv 1981; 392:1-6 “The tumour forms a large firm mass, with a more or less uneven surface. The fibrous substance which constitutes the greater part of it is of a greyish white colour, extremely hard, and as firm as fibro-cartilage. Large portions of the tumour are made up entirely of this mass, but in some parts are cavities or clefts not lined with a distinct membrane. These cavities contain but little fluid; for either their parietes, which are hard like fibro-cartilage, and finely polished, lie in close apposition with each other, or a number of firm, irregular laminae sprout from the mass, and form the walls of the fissures; or excrescences of a foliated or wartlike form sprout from the bottom of the cavities and fill up their interior. These excrescences are perfectly smooth on their surface, and never contain cysts or cells. The laminae lie very irregularly, and project into the cavities and fissures like the folds of the psalterium in the interior of the third stomach of ruminant animals.” -Johannes Peter Müller Evolving concepts on classification

“…the disease is perfectly innocent” Müller (1838) Benign

• Lee and Pack (1931) reported 5 recurrences in 91 cases with available clinical outcome • White (1940) reported recurrence and subsequent metastasis of a case

Cooper and Ackerman (1943) proposed Benign Malignant

Treves and Sunderland (1951) reported 18 of 77 tumours could not fit in either category

Treves and Sunderland (1951) proposed Benign Borderline Malignant Histological assessment

Norris and Taylor (1967) – 94 cases Proposed criteria: 1) Contours (margins) and size of tumour 2) Degree of mitotic activity 3) Cellular atypism

Oberman; Hart et al (1965;1978) Suggested stromal overgrowth as an additional adverse prognostic factor

Ward and Evans (1986) Specified objective for stromal overgrowth, assessment of cellularity and atypia in semi-quantitative way

Tan et al (2011) Quantitative weightage of risk based on stromal atypia, mitotic rate, overgrowth and surgical margins Breast phyllodes tumours

Core biopsy diagnosis

15 Core biopsy diagnosis

• Important modality in pre-operative diagnosis of breast lesions. • Diagnosis of unambiguous fibroadenoma is usually accomplished without difficulty. • Challenges ~ – Cellular fibroepithelial lesions – Spindle cell lesions

16 16 Core biopsy diagnosis of cellular fibroepithelial lesions – prediction of phyllodes tumour Author Reference Key findings predicting phyllodes tumour

Jacobs et al Am J Clin Marked stromal cellularity, mitoses in moderate stromal Pathol 2005; cellularity, Ki67 & topoisomerase IIα indices 124: 342-354 Lee et al Histopathology Stromal cellularity ≥ 50% stroma, stromal overgrowth, 2007; 51: 336- fragmentation, adipose within stroma 344 Resetkova Breast J 2010; No predictive value of clinical, radiologic or pathologic et al 16:573-80. data Suggested follow-up alone for a patient subset Jara-Lazaro Histopathology Marked stromal cellularity/atypia, stromal overgrowth, et al 2010; 57: 220- mitoses ≥ 2 per 10 hpf, ill-defined lesional borders, 232 Ki67 & topoisomerase IIα indices ≥ 5%, reduced CD34 staining Yasir et al Am J Clin Mitoses, stromal overgrowth, fragmentation, Pathol 2014; adipose infiltration, heterogeneity, 142: 362-369 subepithelial condensation, nuclear pleomorphism Stromal hypercellularity Core biopsy Mitoses features

Ill-defined borders & adipose in stroma

Adipose infiltration Fragmentation Can digital pathology help? No

Journal of Clinical Pathology 2018;71:672-679. . Audit of core needle biopsies of 69 equivocal FELs. . Moderate agreement observed among breast specialists (kappa 0.44). . Digital point counting of stromal cellularity and epithelial:stromal ratio did not aid in the classification of these lesions.

19 Can molecular pathology help?

20 Launched 31 October 2018 Can molecular pathology help?

• Potentially, possibly, probably……… • Adjunctive tool. • Does not replace histological evaluation. • Awareness of context, and what question the molecular tool is able to answer.

Declaration ~ No commercial or financial interests in the FibroPhyllo Tissue test

22 Spindle cell lesions on core biopsy

• Keep a broad range of differential diagnoses. • Clinicoradiological findings are important. • Adjunctive studies are helpful, but beware of pitfalls and limitations on small samples. • Final diagnosis usually rendered on excision.

23 Breast phyllodes tumours

Grading & Prediction of Biological Behaviour

24 Phyllodes tumour

WHO Classifications (& Grading) 1981, 2003, 2012 Stromal nuclear atypia assessment is one of the histological criteria for grading phyllodes tumours SGH Pathology Phyllodes tumour

New classification (and grading) to come ~ 2019 WHO classification of breast tumours 2012 Tumour borders

circumscribed permeative

29 Stromal cellularity

mild moderate marked

30 Stromal atypia

marked

mild moderate

31 Mitotic activity

Benign Borderline Malignant < 5 5 to 9 ≥ 10 mitoses/10hpf mitoses/10hpf mitoses/10hpf

32 Stromal overgrowth

Absent Present

Low power (40x) magnification, x10 eyepiece, x4 objective

33 Phyllodes tumours: prediction of biological behaviour

• Grade correlates with behaviour. • Grade assignment is imperfect: – Stromal hypercellularity, atypia, mitoses, overgrowth, borders. • Questions: – Does each histological parameter have equal importance? – Can we determine if some parameters have a greater weightage in predicting behaviour? – Is there an objective scoring system that can define behaviour?

34 J Clin Pathol. 2012 Jan;65(1):69-76. . 605 women with phyllodes tumours diagnosed at SGH Pathology between 1992 and 2010. Phyllodes Benign Borderline Malignant Total tumour (%) (%) (%) (%)

Number 440 (72.7) 111 (18.4) 54 (8.9) 605 (100) Recurrence 48 (10.9) 16 (14.4) 16 (29.6) 80 (13.2)

Mean and median times to recurrence 29.8 and 24.6 months respectively. A : Atypia M: Mitoses O: Overgrowth S : Surgical margin https://mobile.sgh.com.sg/ptrra/

Concordance index 0.904 J Clin Pathol. 2014 Aug;67(8):748-50.

Concordance index 0.933

J Clin Pathol. 2016 Dec;69(12):1124-1126.

Concordance index 0.863 259 concordance index of 0.84 USCAP 2017 abstract Phyllodes tumours: prediction of metastases

• Metastases are rare, ≤ 2% of all tumours. • Occur almost exclusively in malignant PT. • Predictors of metastases ~ – Age >50 yrs, stromal overgrowth, diffuse marked atypia, necrosis, mitoses ≥10/10hpf (Mod Pathol. 2018 Jul;31(7):1073-1084.) – Large tumours (>9cm) with heterologous elements (Virchows Arch. 2018 Apr;472(4):615-621.)

42 Lung Metastatic phyllodes tumours

Lymph node

Gastric biopsy Breast phyllodes tumours

Overcoming classification challenges

44 Cellular fibroadenoma vs phyllodes tumour

• Cellular fibroadenoma ~ – Typical fibroadenoma but with increased stromal cellularity. – Degree of stromal cellularity for this designation is subjective, varying among pathologists. – Stromal cellularity tends to be increased in fibroadenomas in the young. – Lacks leaf-like fronds of phyllodes tumour. – Histological features overlap with the juvenile fibroadenoma.

45 45 Cellular fibroadenoma

46 Cellular fibroadenoma

47 Juvenile fibroadenoma

48 Juvenile fibroadenoma

49 Cellular fibroadenoma vs phyllodes tumour

• Phyllodes tumour ~ – Exaggerated intracanalicular growth pattern. – Elongated epithelium lined arcs. – Broad, well-developed stromal fronds. – At least mild stromal hypercellularity.

50 50 Benign phyllodes tumour

51 51 52 Atlas of Differential Diagnosis in Breast Pathology, Springer 2017 Genomic analysis of fibroadenomas and benign phyllodes tumours, International Fibroepithelial Consortium

53 • Benign phyllodes tumours possessed significantly more mutations in MED12, TERT, RARA, FLNA, SETD2, RB1 and IGF1R, compared to fibroadenomas, both conventional and cellular. • Potential role of genomics to assist in separating fibroadenomas from phyllodes tumours. 54 Metaplastic carcinoma vs malignant phyllodes tumour vs sarcoma

55 Atlas of Differential Diagnosis in Breast Pathology, Springer 2017 55 Phyllodes tumour, Metaplastic carcinoma Sarcoma malignant 57 Division of Pathology 58 • 17 cases of breast sarcoma and 45 cases of malignant PT. • No significant difference in survival outcomes. • Similar clinicopathological features. • Suggesting shared biological relationship.

59 59 Breast phyllodes tumours

Role of molecular data in grading & classification

60 Molecular grading

Two-tiered and three-tiered grading schemes

Karyotyping (Dietrich, 1997) Benign Malignant LOH analysis (Wang, 2006) Low/Intermediate Malignant

CGH (Lae, 2007) Benign Borderline/Malignant array CGH (Jones, 2008) Benign/Borderline Malignant Microarray (Ang, 2010) Benign Borderline Malignant

Grading of phyllodes tumours Nat Genet. 2014 Aug;46(8):877-80.

Nat Genet. 2015 Nov;47(11):1341-5.

62 MED12 mutations in breast fibroadenoma

• MED12 is located on the X chromosome. • Frequent MED12 exon 2 somatic mutations have been found previously only in uterine leiomyoma (UL). • MED12 mutation spectrum observed in fibroadenomas was nearly identical to that of UL in both exon location and variant codon preference. • Possibility that MED12 exon 2 mutations could be associated with hormonal expression. • MED12 in phyllodes tumours.

63 Genomic landscapes of breast fibroepithelial tumours

Tan J et al. Nat Genet. 2015 Nov;47(11):1341-5. A proposed model of the genomic progression of breast fibroepithelial tumours

TERT

Tan J et al. Nat Genet. 2015 Nov;47(11):1341-5. Multiple papers on the genomics of fibroepithelial tumours have been published 66 What’s the clinical relevance? – Genomics based classification of breast fibroepithelial lesions, enhancing diagnostic accuracy ~ • Differentiating FA from PT (J Pathol 2016;238:508-518) • Differentiating PT from other spindle cell tumours (APMIS 2016;124:356-364) • Differentiating malignant PT from metaplastic carcinoma (Pathology 2017;49:786-789) – Discovery of candidate therapeutic targets in borderline/malignant PT ~  PIK3CA activating mutations  EGFR amplifications – MED12 mutations correlated with improved disease free survival (J Clin Pathol 2015;68:685-91; Genes,Chromosomes&Cancer 2016;55:495–504) – MED12 and RARA mutations linked to hormone receptor signaling

67 SGH Pathology Acknowledgements Breast research team Clinical Research SGH • Dr Aye Aye Thike • Mr Jeffrey Lim • Dr HuiHua Li • Ms Valerie Koh • Ms Nur Diyana Bte Md Nasir Duke-NUS/NCCS • Dr Joe Yeong • Dr Bin-Tean Teh • Benjamin Loke • Dr Patrick Tan • Chen Xiaoyang • Dr Steve Rosen • Johnathan Lim • Dr Jing Tan • Dr Cedric Ng Breast service team • Dr Choon Kiat Ong • Dr Angela Chong • Dr Weng Khong Lim • Dr Inny Busmanis • Dr Guan Peiyong • Dr Jabed Iqbal • Dr Syed Salahuddin • Dr Benjamin Yongcheng Tan Breast Surgical Oncology • Dr Tze Wei Chng • Dr Kong Wee Ong • Dr Timothy Tay • Dr Benita Tan • Dr Yirong Sim Anatomy, Yong Loo Lin • Dr Sue Zann Lim School of Medicine, NUS Dr Boon Huat Bay, Dr George Yip International Consortium of Breast Fibroepithelial Tumours Hong Kong Dr Alex Tsang Japan Dr Julia Tsang Dr Naoki Kanomata Dr Gary Tse Dr Oi Harada Dr Rieko Nishimura Italy Dr Yasuyo Ohi Dr Maria Pia Foschini Dr Rin Yamaguchi

UK Bangladesh Prof Elinor J Sawyer Prof S M Khodeza Nahar Begum Prof Mohammed Kamal

UAE Taiwan Dr Aaron Han Dr Chih-Jung Chen

Singapore Dr Kenneth Chang Dr Mihir Gudi Malaysia Dr Gay Hui Ho Dr Norraha Abd Rahman Dr Derrick Lian Dr Kean Hooi Teoh Dr Preetha Madhukumar Prof Phaik Leng Cheah Dr Kong Wee Ong Dr Benita Tan Prof Patrick Tan Philippines Australia Dr Veronique Tan Dr Emmanuel dela Fuente Prof Bin Tean Teh Prof Cheok Soon Lee Dr Chow Yin Wong Dr Wei Sean Yong Thank you!