81 - 92: Extranodal Lymphoproliferative Processes

The diagnosis of primitive extranodal (EN) non-Hodgkin lymphoma (NHL), as well as their classification and proper treatment, are a common challenge in the routine assessment of lymphoproliferative processes. The term “primitive” is used to distinguish EN-NHL from secondary involvements of EN sites by nodal NHL [1]. EN-NHL may display a variety of morphological features, molecular alterations, and clinical presentations. They can arise in different usual or unusual sites, including the salivary glands (SG) and oral cavity, lung and upper respiratory tract, thyroid, breast, gastrointestinal tract, bone and soft tissues, orbit, and central nervous system [1]. The organ of EN-NHL onset, other than the specific entities, is important for the natural history and prognosis of the disease. EN-NHL is often related to different aetiologies and molecular mechanisms, and may be indolent or aggressive; the corresponding organ of onset shows distinct histopathological features, requires specific staging, follows specific patterns of dissemination and relapse, and requires different treatments [2]. The two most common histotypes are EN marginal zone lymphoma (MZL), also called “mucosa-associated lymphoid tissue” (MALT), and diffuse large B-cell lymphoma (DLBCL) [1]. MALT accounts for 5-8% of all NHL and is characterized by the acquisition of lymphoid tissue in organs that do not contain it physiologically, such as the stomach, conjunctiva, skin, thyroid, and SG [3]. This is often due to autoimmune diseases, in particular Hashimoto's thyroiditis and Sjögren's syndrome, or bacterial infections responsible for chronic inflammations, such as Helicobacter pylori[1]. Associations between Borrelia burgdorferi infections and cutaneous NHL or Chlamydophila psittaci infection and ocular adnexal NHL are also known. MALT is usually a self-limiting disease - only in rare cases, and after a long duration, does it disseminate to other distant organs [1]. The median age of MALT onset is the sixth decade; patients have a good performance status and the prognosis is generally favourable, with a 75-80% survival at 10 years. MALT arising in the thyroid or the stomach is associated with a better prognosis than when it affects the SGs or the lungs [3]. The treatment for MALT depends on the organ involved; there are many treatments available, such as local therapy, surgery, radiation therapy, chemotherapy alone or combined with biological or antimicrobial therapies. DLBCL clinically appears as nodules or masses with a short clinical history [2]. Like the MALT counterpart, DLBCL is a mainly localized process, although in some localizations (ocular globe, testis, kidney, and paranasal sinuses), it can disseminate to the brain, hence requiring a timely diagnosis and specific prophylaxis to prevent this complication [4]. EN-NHL requires different diagnostic approaches based on the localization, whereas not all sites can be evaluated by fine-needle cytology (FNC). The SG, thyroid, lung, breast, soft tissues, and orbit are the anatomical sites most frequently investigated by FNC [5].

SG NHL account for about 3% of all SG tumours [6,7]. The parotid gland is the most commonly involved one, accounting for about 80% of cases, followed by the submandibular (16%), sublingual (2%), and minor SG (2%) [6]. SG NHL mainly occurs in adults, with a female prevalence [7]. In some cases, it may present with facial paralysis and pain, although it appears most often as a slow growing and painless mass [6]. About 20% of SG NHL patients have a history of Sjögren's syndrome, with benign lymphoepithelial lesion (LEL) or myoepithelial sialoadenitis (MESA) [7]. MESA is considered a precursor of NLH [7] with a risk of developing B-cell NHL 40-fold higher in affected patients. MESA is generally characterized by a lymphoid infiltrate and islands of epithelial-myoepithelial cells [6,8]. The latter are nests of ductal and occasional acinar cells intermingled with small lymphocytes (Fig. 1). Hyaline material of the basal lamina is often present. In minor SG, the cellular components are similar, although the epithelial-myoepithelial islands may be absent. Over time, the lymphoid infiltrate progressively replaces the acinar tissue, sparing some of the ducts. This results in a complete atrophy of the gland and the formation of organized lymphoid tissue with reactive follicles. Most cases of EN NHL arising in the SG are low-grade NHL (MALT) and DLBCL [8,9]. For a long time, SG MALT was underdiagnosed compared to DLBCL, which is more easily recognizable by its cytological atypia; however, with the advent of the immunocytochemistry (ICC) and molecular methods, the diagnosis of SG MALT in the context of MESA has increased [8]. FNC of SG MALT is generally performed at the time of full development of the process. Smears show a relatively polymorphous cell population of small lymphocytes, follicular centre cells and histiocytes (Fig. 2). Fibroblasts and endothelial cells may also occur. The small lymphocytes generally have dense, compact chromatin, and nucleoli are absent. Monocytoid features and nuclear membrane irregularities are seldom observed, clear cytoplasm may be observed (Fig. 3), and mitoses are absent. The SG MALT FNC diagnosis mainly depends on the clonality assessment by flow cytometry (FC) or molecular testing, otherwise an FNC diagnosis is almost impossible. SG DLBLC FNC shows cytological features corresponding to the nodal counterpart [see Chapter 5, this vol., pp. 52-59] and the application of ancillary techniques leads to similar results. EN DLBCL cytological atypia is generally evident and the diagnosis of malignancy may be straightforward. Conversely, the differential diagnosis with poorly differentiated carcinoma or other malignancies may be difficult and depends on ICC or FC.

Thyroidal lymphoid infiltrate mainly occurs in Hashimoto thyroiditis (HT). Long-standing HT causes shrinking and atrophy of the thyroid with progressive follicle loss. HT generally shows high levels of serum antiperoxidase and antithyroglobulin autoantibodies; an increase in serum thyroid-stimulating hormone indicates concomitant hypothyroidism. During its evolution, HT may also lead to diffuse, symmetrical or asymmetrical enlargement of the gland and eventually to the formation of nodules, which may be requested for FNC. Primary thyroidal NHL (PTL) is a possible and rare complication of HT, whereas half of PTLs arise without an HT background [10,11,12]. MALT and DLBCL are the most frequent subtypes. DLBCL roughly comprises half of all cases and MALT approximately 20% of PTLs [10,11,12]. Other rare PTL subtypes are follicular lymphoma, small lymphocytic lymphoma/chronic lymphocytic leukaemia (SLL/CLL) and Hodgkin lymphoma (HL) [2,10,11,12]. MALT and DLBLC FNC show cytological features corresponding to the LN counterpart [see Chapter 5, this vol., pp. 52-59] and the application of ancillary techniques is also similar. Differential diagnoses involve florid HT (Fig. 4) and anaplastic thyroid carcinoma, respectively [13,14,15,16]. MALT FNC should be suspected when dealing with a long-standing HT that slowly and progressively grows rather than shrinks. FNC of thyroidal MALT generally show a monomorphous population of lymphocytes, whereas more polymorphous presentations may occur (Fig. 5). Hurthle or follicular cells are absent. The FNC diagnosis mainly depends on FC detection of a quantitatively relevant light chain restriction or on molecular testing [13,14,15]. Thyroidal DLBCL generally has an increasingly worsening clinical presentation and the clinical differential diagnosis with anaplastic thyroid carcinoma is indicated, mainly when dealing with older patients [16]. Thyroidal DLBCL FNC does not show specific cytological features and the diagnosis depends on an ICC or FC assessment of lymphoid differentiation.

The breast may be involved through primary, EN, lymphoproliferative processes or by secondary localizations of leukaemia or systemic NHL [17,18,19,20,21,22,23,24]. Intramammary LN can also be involved by NHL, but this is a rare event [25,26]. Breast implant-associated anaplastic large-cell lymphoma (BI-ALCL) may rarely arise around breast implants. Non-lymphomatous reactive processes that may occur in the breast are reactive intramammary LN and, more rarely, sclerosing lobulitis [27,28]. As for NHL, the diagnosis of primary breast lymphoma (PBL) is limited to patients without evidence of other localizations of the disease; these represent 2% of EN NHL and less than 1% of all breast malignancies [17,18,19,20,21,22,23,24]. Conversely, secondary NHL involving the breast (SBL) is more common [17,18,19,20,21,22,23,24]. The clinical presentation and imaging of reactive processes and NHL of the breast are quite variable [29]. Intramammary LN has typical ultrasound features but may be confused with fibroadenoma (Fig. 6) [29]. The rare sclerosing lobulitis typically associated with diabetes mellitus has a variable presentation, with either monolateral or bilateral lumps, with or without an ill-defined mass. Corresponding smears show relative polymorphous lymphoid cells similar to those observed in intramammary LN with the presence of occasional small groups of benign ductal cells (Fig. 7). Finally, PBL and SBL imaging can be similar to that of breast carcinoma, showing hypoechoic lesions that may also overlap with medullary carcinoma. Moreover, PBL and SBL may show calcifications and/or speculated borders on mammography, which add further diagnostic difficulties [29]. FNC features of the different entities reported above should be evaluated once more in close connection with clinical and imaging data. For instance, the FNC of a clinically and ultrasound suspected fibroadenoma, showing lymphocytes and follicular centre cells, is most likely a reactive intramammary LN. Or a rapid bilateral breast enlargement likely occurs in patients suffering from leukaemia or NHL, mainly myeloid leukaemia and Burkitt NHL, respectively. Cytological features of breast involvement from NHL have been rarely reported and described as similar to the LN counterparts [24]. Attention should be paid to DLBCL, as it may simulate a breast carcinoma at the clinical and mammography evaluation. BI- ALCL rarely occurs in women with breast implants. BI- ALCL may be clinically subtle because it is associated with late seroma that is a benign reactive process in many cases that may occur in BI. BI-ALCL grows by infiltrating the periprosthetic capsule; the cytological and phenotypical features are those of T-cell or null, CD30+, AlK-negative ALCL [see Chapter 4, this vol., pp. 34-51]. Cytological identification of diagnostic cells may be challenging because of the peculiar anatomical context and the intermingled inflammatory reactive cells [30,31,32].

Lymphoproliferative lesions are the most common primary orbital tumours in older adults, with a slight female prevalence [2,33,34,35,36,37]. These lesions represent a spectrum of disorders that include inflammatory pseudotumours, typical and atypical lymphoid hyperplasia, and NHL [2,33,34,35,36,37]. The latter more frequently arise from the lachrymal glands, with MALT being the most frequent histotype. Corresponding diagnoses depend on a multidisciplinary approach that includes clinical data, imaging and pathology. Orbital lymphoproliferative lesions may be secondary or may arise primarily in the orbit [37]. Possible presentations are palpable masses, proptosis, and mildly restricted ocular motility; pain is an uncommon symptom in orbital NHL, at variance with the pseudotumour, which manifests with acute pain. Most lesions are unilateral (>50% of cases) and are often extraconal. Lacrimal glands are involved by lymphoproliferative processes in nearly 40% of cases [34,35,36,37]. At CT or MR imaging, approximately half the lesions are diffuse and ill defined, with the other half appearing as a smooth, circumscribed mass; uniform enhancement at MR is characteristic. An atypical feature of lymphoproliferative processes is their tendency to mould around the globe, the optic nerve, and orbital wall. The NHL shaped around the latter may result in bone remodeling; osseous erosion is quite rare, although it may occasionally occur with DLBCL. FNC may be performed beneath the roof or below the floor of the orbit to reach the lachrymal gland area or the conus, respectively, and all the other localizations according to their anatomical growth with a transconjunctival or transcutaneous approach. The procedure has to be performed by an ophthalmologist (Fig. 8); the role of the cytopathologist should be focused on smearing, ROSE, and material management. FNC of orbital lymphoproliferative lesions shows a variable monomorphism depending on the different corresponding lesions. Pseudotumour FNC may be variably cellular; smears are generally polymorphous showing lymphocytes, plasma cell histiocytes, and fibroblasts (Fig. 8). Eosinophils and vascular fragments may be present [38]. NHL shows the cytological features of the corresponding LN entities. Cytological criteria and ancillary techniques are almost the same as those described for LN, with the significant additional limitation of generally scanty diagnostic material mainly when obtained from posterior lesions.

Primary pulmonary lymphoma (PPL) refers to the presence of clonal lymphoid proliferations affecting 1 or both lungs and/or bronchi in a patient without evidence of extrapulmonary NHL at diagnosis or during the subsequent 3 months. PPL are mainly classified into 2 categories: pulmonary marginal lymphoma (PML) and DLBCL (PDLBCL) [1]. PML is the most common primary lung NHL, representing 70-90% of all PPL, whereas it accounts for less than 0.5-1% of all primary lung neoplasms [1]. Because nearly half the patients are asymptomatic and are identified incidentally at imaging, the diagnosis of PML is usually made at a late stage [39,40]. CT-guided FNC is routinely used to diagnose lung nodules, masses or thickening and PPL may occur [39]. PML FNC has been described as a bland lymphoid proliferation represented by small- to medium-sized lymphocytes with slightly irregular nuclei and dispersed chromatin. Monocytoid cells with pale cytoplasm, plasma cells and a few follicular centres are also present. LEL, previously described in the Salivary Gland section of this chapter, here are represented by bronchial cells intermingled with lymphocytes, and typical of MZL of other districts, may be scanty or absent in PML. Epithelioid and multinucleated cells in a granulomatous pattern may occur [39]. The FNC diagnosis of PML can be difficult or even impossible because of the similarities with reactive lymphoid hyperplasia and complexity in detecting LEL. Therefore, ROSE and material management for ancillary techniques are essential. In the absence of defined cytological atypia, clonality assessment by FC or PCR is indispensable for malignancy assessment of these lesions. Regarding classification, trisomy of chromosome 3 detectable by FISH (Fig. 9) is an effective procedure on FNC, followed by CD43/CD20 co-expression (Fig. 9). Cytokeratin 7 ICC may be helpful to reveal LEL [39,41]. PDLBCLs represent a small percentage of PPLs; affected patients complain of respiratory and/or systemic symptoms [1]. FNC features are similar to those previously described in other locations, and the differential diagnosis is not made with reactive lesions but with lung carcinoma or other malignancies. The diagnosis must be based on ROSE and cell block techniques for an appropriate ICC panel. Other histotypes, such as small lymphocytic pulmonary lymphoma or pulmonary HL, are rare entities; only single cases or small series have been reported in the literature [42,43].

Pleural, peritoneal and, more rarely, pericardial effusions occur in approximately half of patients with lymphoma. With the exception of the rare primary effusion lymphoma (PEL), they unusually represent the first clinical manifestation of lymphoma [44,45,46]. The main causes of effusions in lymphoma are infections caused by disease-related or iatrogenic immunodeficiency and serous involvement from NHL or leukaemia. Mediastinal LN enlargements (LNe), increased vascular permeability, and postradiation fibrosis that hamper lymphatic drainage may also cause effusion in lymphoma patients. Other causes are congestive heart failure, kidney or liver deficiencies, and even secondary neoplasms [46]. Pleural effusions represent 80% of serous involvement by NHL, followed by peritoneal (15%) and pericardial (5%), with PEL being extremely rare. In order of incidence, lymphoma-related effusions are NHL, leukaemia, myeloma, very rarely HL, with a high incidence of high-grade and T-cell NHL and a low-incidence of HL when compared to their epidemiologic incidence [46,47,48,49,50,51,52,53,54,55,56,57,58,59,60]. A cytological diagnosis of lymphoma-related effusions may be difficult because high cellularity and nuclear atypia do not necessarily correlate with serous involvement by NHL; in fact, reactive lymphocytosis in effusions may be highly cellular and may show nuclear atypia. Conversely, NHL-related effusions may be less cellular and with mild or absent cytological atypia. Therefore, effusions with lymphocytosis in NHL patients cannot be diagnosed without ancillary techniques.

Different reactive processes, mainly viral infections, may cause effusions with serosal lymphocytosis. Corresponding cytological samples (cytospin or cell block) generally show a variable number of mesothelial cells, histiocytes, and lymphocytes. Reactive effusions with lymphocytosis may be extremely cellular and warningly monomorphous when compared to the polymorphism of the reactive LNe counterparts. Reactive lymphocytes are mainly T cells, showing the corresponding phenotype (CD3+, CD4/CD8+, CD5+) by FC or ICC on cell blocks or cytospins (Fig. 10) [46,61,62,63].

SLL/CLL is a frequent cause of effusion, and the cytological features have previously been described [see Chapter 4, this vol., pp. 34-51]. Corresponding cytological samples show a variable number of mesothelial cells intermingled between SLL/CLL cells. The cell phenotype by ICC on cytospins or by FC is CD5+, CD19+, CD23+, CD10-, FMC7-, with light chain restriction. CD19/CD5 co-expression and specific cytological features are the clue to the diagnosis (Fig. 11). Secondary tumour cells (mainly from lung tumour) causing effusions may be hidden by the concomitant SLL/CLL cells [64,65]. FL, MZL, and mantle cell lymphoma (MCL) may also cause effusions (Fig. 12)[[44,45,46,47]; see Chapter 4, this vol., pp. 36-39]. DLBCL and BL have a high incidence of effusion, which may reach 35% in BL [ [51,53]; see Chapter 4, this vol., pp. 34-51]. Because of their specific cytological features, a cytological diagnosis may not necessarily require ancillary techniques (Fig. 13).

T-cell NHL determines serous effusions more frequently than B-cell NHL [46]. This high incidence is maintained by precursor T-lymphoblastic lymphoma and leukaemia. Conversely, peripheral T-cell NHL rarely causes effusions [54,55,56]. Corresponding cytological features and diagnostic criteria have been previously described [see Chapter 4, this vol., pp. 34-51].

PEL is an extremely rare NHL, mainly reported in immunodepressed patients, without nodal or EN masses [66]. PEL mainly occurs in AIDS patients and is caused by HHV8 superinfection [67]. It is considered to be of B-cell origin, with unexpressed B-cell and T-cell markers. Activation markers (CD30) and plasma cell differentiation (CD138) may be expressed. Like other high-grade NHL, FC may be ineffective and a cytological diagnosis will rely on microscopic features and leucocyte common antigen positivity on cell block [68].

Malignant involvement of the subarachnoid space occurs in 5-8% of patients with malignancies [69] and the cytological evaluation of cerebrospinal fluid (CSF) is an essential step for the diagnosis of leptomeningeal involvement. The most common malignancies that cause leptomeningeal involvement are lung and breast cancer, melanoma, NHL, and leukaemia. Inconclusive diagnoses on CSF are often due to scant cellularity or poor preservation or blood contamination of the sample. Leptomeningeal involvement occurs in 5-10% of patients with NHL, either at presentation, at a later stage of the disease course, or at relapse [69]. Leptomeningeal involvement is more common than parenchymal brain involvement by NHL [70]. The features generally observed are a monomorphous dispersed population of atypical cells larger than normal lymphocytes, irregular nuclear contours, abnormal chromatin, and nucleoli. The differential diagnosis is a reactive lymphocytosis composed of small, mature lymphocytes and larger, activated, so-called atypical lymphocytes. In some cases, a definitive diagnosis is not possible without lymphoid marker evaluation by ICC on cytospins (Fig. 14) or FC [71,72]. In patients with acute leukaemia, either lymphoid or myeloid, it may be sufficient to identify the presence of blasts in CSF; further phenotypization (lymphoid vs. myeloid) can be performed on peripheral blood and bone marrow. PCR may be useful in selected cases and can be performed on archival and fresh CSF samples [73].