Update in salivary gland cytopathology: Recent molecular advances and diagnostic applications

Pusztaszeri MP, Faquin WC. Seminars in diagnostic pathology 2015 Jul 31 (Vol. 32, No. 4, pp. 264-274)

Contents of the article

• Introduction

• Recent molecular advances in SGTs

• Uncommon and recently recognized entities

• Conclusions

Introduction

• Fine needle aspiration biopsy of

salivary gland lesions

: high sensitivity - 86 to 100%

: high specificity – 90 to 100%

• Accuracy of FNAB in distinguishing

benign from malignant : 81 to 100%

• But , the accuracy of FNAB of

salivary gland in subtyping a

neoplasm

: 48-94%

Why salivary gland FNAB is challenging?

• 37 distinct epithelial neoplasms of salivary gland (WHO 2005)

• Intratumoral heterogeneity

• Morphological overlapping among many salivary gland tumours

Therefore, cytomorphology alone, without the use of ancillary studies has limitations.

Translocations and fusion genes

• The translocation t(3;8) in Pleomorphic adenoma, has been known for almost 2 decades, translocations in other SGTs have been discussed in this article.

• In addition to their diagnostic role, they may also represent prognostic markers and possibly therapeutic targets in the near future

• The current treatment of patients

with SGT is mainly restricted to

surgery and/or radiation therapy,

and only limited data is available on

the role of conventional systemic

and targeted therapies for patients

with advanced disease.

Pleomorphic adenoma• Most common SGT of all sites in both adults

and children(60%).

• Cytological features

1) Epithelial cells, myoepithelial cells(spindle, epithelioid, plasmacytoid, and clear cell),

2) fibrillary chondro-myxoid matrix (with frayed edges and embedded myoepithelial cells)

Fibrillary myxoid matrix

Myoepithelial cells

• A subset of PAs may lack or have scant chondro-myxoid matrix (i.e., cellular PA), making it difficult to distinguish from other myoepithelial and “basaloid” neoplasms.

• Metaplastic changes with squamous, sebaceous, oncocytes or mucinous cells may mimic ‘Mucoepidermoid Carcinoma ’

• Hyaline like globules may mimic adenoid cystic carcinoma

Pleomorphic adenoma with a hyaline globule

Myoepithelial cells with bland round nuclei

Pleomorphic adenomaMost common translocation t(3,8)(p21;q12)Genes involved PLAG1, CTNNB1, LIFRPrevalence 50-60%

• The translocation typically leads to upregulation and overexpression of PLAG1.

• PAs (94%) are strongly immunoreactive for PLAG1

• PLAG1 is negative in the most common

(SGCs), including AdCC, MEC, and

acinic cell carcinoma (ACC).

• In addition to PLAG1, HMGA2 gene are

found in a minor subset of PAs (10%).

• Cytologically, it can be difficult to distinguish cellular PAs from other basaloid neoplasms, including BCA, basal cell adenocarcinoma, and AdCC. Therefore, immunocytochemistry and/or FISH for PLAG1 can be useful in this setting

Carcinoma-ex-pleomorphic adenoma

• Carcinoma arising in a primary or recurrent PA

• 12% of Salivary gland carcinomas

• Same genetic abnormality as in its benign PA precursor including PLAG1 and HMGA2.

cluster of malignant ductal cells in Ca-Ex-PA with dark granular chromatin and high nuclear-to-cytoplasmic ratio

• But also, accumulates additional aberrations that presumably lead to the malignant transformation

• Immunochemistry and/or FISH for PLAG1 may help to discriminate CA-ex-PA from other high-grade SGCs arising de novo

Mucoepidermoid carcinoma• Most common SGC in both adults

and children, representing approximately 30% of SGCs

• Important to distinguish between low-grade and high-grade MECs due to major differences in prognosis, with 90% and 40% 5-year survival, respectively

• Cytomorphology of low grade MEC:

Mucous cells, epidermoid/squamoid cells, and intermediate cells with extracellular mucin.

• Cytomorphology of high grade MEC :

Same as low-grade plus overt cytologic malignancy

Goblet type mucus cells

Intermediate cells

Mucicarmine stain highlights the mucin content ina goblet cell from a LGMEC

Mucoepidermoid carcinomamost common translocation t(11;19)(q21-22;p13)genes involved MAML2-CRTC1 gene

fusion

•The presence of the CRTC1–MAML2 fusion is specific to MECs,• It can also be used as a diagnostic tool to differentiate high-grade MECs from other high-grade SGCs or to distinguish oncocytic MECs from other oncocytic neoplasms including Warthin tumor

Adenoid cystic carcinoma

• 10% of all SGTs

• Indolent growth pattern

• Frequent recurrences, marked neurotropism, late onset of metastasis

• poor long-term survival (approximately 30–40% at 10–20 years)

• Cytomorphology of adenoid cystic carcinoma:

1) Basaloid cells with hyperchromatic and often angulated nuclei

2) Acellular hyaline matrix forming globules with sharp borders

Cibriform pattern in adenoid cystic carcinoma

Well demarcated Hyaline globiles with small basaloid cells in adenoid cystic carcinoma

• Solid subtype, can be difficult to diagnose on FNAB because of lack of the characteristic matrix and overlapping morphological features with PAs, BCA, basal cell adenocarcinoma, myoepithelioma, epithelial myoepithelial carcinoma, and PLGAs

• MYB overexpression can be used as a diagnostic marker for AdCC

Adenoid cystic carcinomamost common translocation t(6;9)(q22-23;p23-24)genes involved MYB-NFIB gene fusion

Basaloid cells in AdCC with bland nuclear features and show strong nuclear immunostaining for MYB.

Mammary analog secretory carcinoma

• Rare SGT first described in 2010 by Skalova et al

• Occurs more commonly in males and at extraparotid sites.

• The morphology, immunohistochemical, and molecular profiles of MASC are identical to secretory carcinoma of the breast.

• Cytomorphology of mammary analog secretory carcinoma:

1) Histiocytoid-like cells with abundant finely vacuolated cytoplasm

2) Uniform round nuclei with open chromatin and nucleoli

3) Background of pale-staining seromucinous or cystic material

dyshesive large polygonal cells with abundant vacuolated

cytoplasm, and round to ovoid nuclei with small nucleoli

Background shows seromucinous material

• It is the only primary salivary gland tumour

harbouring ETV6 rearrangement.

• Cytologically, MASCs can be confused with

PA or other oncocytic SGTs, including WT,

ACC, and MEC

• The most definitive marker of MASC is

identification of the ETV6 gene

rearrangement, usually by FISH

• Immunohistochemical positivity for mammaglobin , GATA-3, 82 GCDFP-15, and S-100 and negativity for DOG1 are useful.

strong cytoplasmic immunostaining for mammaglobin

Hyalinizing clear cell carcinoma

• Rare low-grade SGC• It typically arises from the minor

salivary glands of the oral cavity of women

most common translocation

t(12;22)(q13;p12)

genes involved EWSR1-ATF1 gene fusion

• Cytomorphology of hyalinizing clear cell carcinoma

1) Large and cohesive epithelial cell clusters with nuclear uniformity

2) Clear cytoplasm, and distinct cell borders

3) scant homogenous fibrous stroma

• Being composed mainly of clear cells, the cyto-histopathologic differential diagnosis of HCCC is very broad and includes:

1) Clear cell oncocytoma, 2) Low-grade MEC, 3) Epithelial–myoepithelial carcinoma4) Clear cell myoepithelioma/myoepithelial

carcinoma,5) ACC,6) Metastatic renal cell carcinoma,7) Squamous cell carcinoma clear-cell variant,8) Melanoma

• HCCC does not contain a myoepithelial cell component or a myxohyaline stroma, and lacks myoepithelial differentiation on immunochemistry

• FISH for the EWSR-1 translocation can be performed on smears or cell-block in order to confirm a diagnosis of HCCC

Cribriform adenocarcinoma of minor salivary gland

• Low-grade SGC, closely related to PLGA

• The most common reported location is the base of the tongue (76%), followed by palate (7%), tonsils (7%), retromolar mucosa (5%), floor of mouth (2%), and upper lip (2%)

• It may be confused with PLGA in minor salivary gland sites and with papillary thyroid carcinoma (PTC) in cervical lymph node metastases.

• In contrast to PTC, however, TTF-1 and thyroglobulin are consistently negative in CAMSG.

Conclusions

• FNAB remains one of the mainstays of the initial diagnosis of SGT

• Cell blocks and/or smears can provide adequate material for ancillary studies such as FISH or next-generation sequencing to detect specific chromosomal translocation

• Immunocytochemistry can be used to detect abnormal oncoproteins resulting from these translocations, such as MYB or PLAG1

• These ancillary studies may also provide important prognostic and therapeutic information for patients with SGT in the future

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