Haematology Watch, Vol.5 , Issue 1.
PERSPECTIVES
Hodgkin Lymphoma
Dr. Usman Hassan, Dr. Sheeba Ishtiaq and Prof. Khalid Hassan
Postgraduate Resident, Department of Pathology, Shaukat Khanum Memorial Cancer Hospital, Lahore
Department of Pathology, Pakistan Institute of Medical Sciences, Islamabad
Introduction
This neoplasm was recognized in the 19th century by Thomas Hodgkin and Samuel Wilks. Samuel Wilks latter named this disease as Hodgkin disease. Now the term Hodgkin lymphoma is preferred as currently Reed Sternberg cells are recog-nized as lymphoid cells most often of B-cell type. There are distinct subtypes of Hodgkin lymphoma but there are few common clinical and histopathological features:
• They usually involve lymph nodes especially cervical lymph nodes.[1]
• Majority of them effect young adults.
• Majority of Hodgkin lymphomas show a population of large cells with large nuclei and prominent nucleoli scattered in the mixed heterogeneous background of reactive inflammatory cells.
• The tumour cells are surrounded by T lymphocytes in rosette like fashion.
Hodgkin lymphoma can be classified broadly in two categories: nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) and classical Hodgkin lymphoma (CHL). This classification was considered necessary because differences in biological behaviour, clinical features, composition of cellular background and also the morphology, immunophenotype and B-cell expression.[2] Also the four subtypes of CHL differ in clinical features, histopathological features and frequency of Epstein Barr Virus (EBV) infection but not in immunophenotypical features.
Nodular Lymphocyte Predominant Hodgkin Lymphoma (NLPHL)
WHO Definition:
NLPHL is a monoclonal B-cell neoplasm characterized by a nodular, or a nodular and diffuse proliferation of scattered large neoplastic cells known as popcorn or lymphocyte predominant (LP) cells. These cells reside in large spherical meshworks of follicular dendritic cell processes that are filled with non neoplastic lymphocytes and histiocytes. [3]
Clinical features and Epidemiology:
NLPHL comprises 5% of all Hodgkin lymphoma and it involves predominantly males in their 4th and 5th decades. Mostly involved lymph nodes groups are cervical, axillary and inguinal. Bone marrow, spleen and mediastinal involvement is not common. [4] Only few patients present with advanced disease. Majority of the patients present with localized peripheral lymphadenopathy (Stage I and II).
Morphology:
Lymph node architecture is partially or totally effaced by nodular or nodular and diffuse pattern. Predominant diffuse pattern is rare. Predominantly the lymph node is involved by small lymphocytes and histiocytes with intermingled large cells having folded and multilobated nuclei. Nuclei contain multiple small basophilic nucleoli. Cells are also called popcorn cells because sometimes nuclei are so much folded that cells resemble popcorns. [5] If there are diffuse areas, they are composed of small lymphocytes and histiocytes in majority. Lymphocytes and plasma cells can be found in the periphery of nodules. [6] Neutrophils and eosinophils are not seen commonly in NLPHL. Sometimes, one may find follicular hyperplasia with progressive transformation of germinal centres (PTGC) adjacent to the lesion. In PTGC, cells of mantle zone infiltrate the germinal centres and blur the demarcation zone between the germinal centre and mantle zone. PTGC is occasional found to precede NLPHL. However it has not been established as a precursor of NLPHL. Sclerosis is infrequently found in primary biopsies but can be found in 45% cases of recurrences.
Immunohistochemistry:
LP cells are positive for CD20, CD79a, CD75, BCL6 and CD45 in nearly all cases. [7] J chain is positive in majority of the cases and epithelial membrane antigen (EMA) in 50% of the cases. OCT2 and BOB1 are consistently co-expressed. [8] CD15 and CD30 is not expressed in nearly all instances, however CD30 can be positive in few cases. Most of LP cells are rimmed by T cells which stain for CD3. [9] The background of NLPHL comprises predominantly of small B cells and CD4+ and CD57+ T cells.
Genetics:
Clonally rearranged immunoglobulin genes (Ig) are common. Latent EBV infection is consistently absent from LP cells.
Prognosis:
It develops slowly and is rarely fatal. It is a treatment responsive disease. Prognosis in low stage (Stage I and II) patients is good with 80% 10 years overall survival time. Advanced disease has an unfavorable prognosis. Progression to large B-cell lymphoma has been reported in 3-5% of cases. [10] Bone marrow involvement is uncommon, but is involved poses a poor prognosis.
Classical Hodgkin Lymphoma (CHL)
WHO definition:
CHL is a monoclonal lymphoid neoplasm composed of mononuclear Hodgkin cells and multinucleated Reed Sternberg cells (HRS) residing in an infiltrate containing a variable mixture of non-neoplastic small lymphocytes, eosinophils, neutrophils, histiocytes, plasma cells, fibroblasts and collagen fibres. In most cases CHL is derived from B cells.
Four histological subtypes are now recognized: lymphocyte rich CHL (LRCHL), nodular sclerosis CHL (NSCHL), mixed cellularity CHL (MCCHL) and lymphocyte depleted CHL (LDCHL). [11] Although there are differences in clinical features and association with EBV, but the immunophenotypic and genetic features of all four subtypes are identical.
Etiology:
EBV has been postulated as a possible pathogenetic factor in CHL but EBV is found in only a proportion of cases especially in MCCHL and LDCHL. HIV infection predisposes to EBV associated CHL. CHL in tropical regions show 100% positivity for EBV. [11]
Epidemiology and Clinical Features:
CHL comprises about 95% of Hodgkin lymphomas. It shows bimodal age curve with first peak in 2nd to 4th decades and second peak in late life. [11] Patients with infectious mononucleosis show higher incidence.
Clinical Features:
CHL mostly involve peripheral lymph nodes like cervical and axillary lymph nodes and also paraaortic lymph nodes. Medi-astinal involvement is also common especially in NSCHL. Splenic involvement is also not uncommon. Bone marrow is involved in 5% of the cases. Most of the patients (60%) present with low stage (Stage I and II) disease. B symptoms like fever, night sweats and significant body weight loss are present in up to 40% of the cases.
Morphology:
Grossly lymph nodes are enlarged and encapsulated. Cut surface shows a fish flesh appearance. In thymus, CHL can be associated with cystic degeneration. Lymph node architecture is effaced by HRS cells and Hodgkin cells (mononuclear cells) admixed with heterogeneous inflammatory background. HRS cells are large cells with at least two nuclear lobes or nuclei and abundant basophilic cytoplasm. Each nucleus have round contours with irregular nuclear outline, pale chromatin and have two prominent eospinophilic nucleoli in two separate nuclear lobes. Perinuclear halo is also a characteristic feature. Large cell having pyknotic reddish nuclei are called mummified cells. These HRS cells comprise only a minority (0.1-10%) of the cellular infiltrate. The composition of reactive cellular infiltrate differs according to the histological subtype. The criteria for diagnosis in secondary site like bone marrow and spleen in a known patient of Hodgkin lymphoma is different. Presence of mononuclear CD30 positive cells, either positive or negative for CD15 is sufficient for the diagnosis of Hodgkin lymphoma. The presence of HRS cells is not necessary. Immunohistochemistry: HRS cells are positive for CD15 and CD30 in membranous pattern with accentuation of the Golgi area of cytoplasm. [9] About 30-40% cases show positivity with variable intensity for CD20. CD79a is less commonly expressed. PAX5 is expressed in majority of the cases but the intensity is weaker than reactive B-cells. The later phenomenon makes distinction of HRS cells easy. The plasma cell transcription factor IRF4/MUM1 is consistently expressed in HRS cells. CD138 is usually absent. The markers which stain LP cells in NLPHL are usually negative in HRS cells. These are CD75, J chain, EMA, Oct2, BOB18
Genetics:
HRS cells contain immunoglobulin gene rearrangements in 98% of the cases and T-cell receptor gene rearrangement in very rare percentage of cases. [12] The expression of EBV varies according to subtype. The highest frequency of expression is found in MCCHL (75%) and lowest in NSCHL (10-40%). In resource poor regions and in HIV infections, EBV expression in CHL is 100%. Conventional cytogenetics and Fluorescence insitu Hybridization show aneuploidy and hypertetraploidy.
Prognosis:
Histological subtype is not an important prognostic factor. Clinical and laboratory parameters predict the prognosis. Staging determines the mode of therapy and chemoradiotherapy has made CHL curable in about 85% of the cases. [13]
Nodular sclerosis Classical Hodgkin Lymphoma (NSCHL)
WHO definition:
NSCHL is a subtype of CHL characterized by collagen bands that surround at least one nodule, and Hodgkin and Reed-Sternberg (HRS) cells with lacunar type morphology.
Epidemiology and Clinical Features:
It is more common in resource rich countries like USA and Europe where it comprises 70% of CHL. The incidence is similar in both genders with peak ages in the range of 15-34 years. Most of the patients present with stage II disease. Mediastinal involvement is seen in 80% of the cases, splenic/or lung involvement in 10% cases and bone marrow involvement in 2% of the cases. About 40% of the patients show B symptoms.
Morphology:
On gross examination, there is a prominent nodularity, dense fibrotic bands and a thickened capsule. Splenic involvement shows scattered nodules within the white pulp. Histologically lymph node architecture is effaced by closely packed nodules surrounded by fibrous bands. Fibrous bands are fibroblastic poor and and are broad. Lymph node capsule is also thickened. NSCHL contains variable number of HRS cells, lymphocytes and other inflammatory cells. [14] Histiocytes, eosinophils and neutrophils are often numerous. HRS cells are lobated with smaller lobes and less prominent nucleoli. Cytoplasm is abundant. HRS cells can be present in large numbers, in which case it can be labelled as syncytial variant. It is thought that grading depends on the proportion of HRS cells and background non neoplastic inflammatory infiltrate (such as number of eosinophils) and the grading predicts prognosis. However this grading is not usually done routinely.
Immunohistochemistry:
Immunophenotype is same as that described for CHL. EBV expression is less frequent (10-40%) than in mixed cellularity CHL. [15]
Prognosis:
NSCHL has an overall better prognosis than other types of CHL. Massive mediastinal disease is an adverse prognostic factor.
Mixed Cellularity Classical Hodgkin Lymphoma (MCCHL)
WHO definition:
MCCHL is a subtype of CHL with scattered HRS cells in a diffuse or vaguely nodular mixed inflammatory background without nodular sclerosing fibrosis.
Epidemiology and clinical features:
It comprises 20-25% of CHL. It is more common in developing countries [16] and in patients with HIV. It more commonly effects males. Median age of involvement is 38 years. No bimodal age distribution is noted. Peripheral lymph nodes are more commonly involved and mediastinal involvement is uncommon. Spleen is involved in 30% and bone marrow in 10% of the cases. B symptoms are frequent. [17]
Morphology:
Lymph node architecture is usually obliterated. Interstitial fibrosis may be seen, but there are no broad collagen bands and lymph node capsule is not thickened. The HRS cells are typical in appearance with typical binucleated cells and prominent eosinophilic prominent nucleoli. [14] Background shows mixed inflammatory infiltrate comprising lymphocytes, eosinophils, plasma cells and histiocytes. Histiocytes may show epithelioid features especially in those cases infected with EBV.
Immunohistochemistry:
Immunophenotype is same as that of CHL. EBV expression is more common (75%). [18]
Prognosis:
Prior to the era of modern therapy, MCCHL used to have worse prognosis than NSCHL and better prognosis than lympho-cyte depleted CHL. These differences are largely disappeared with modern therapy if not completely vanished.
Lymphocyte Rich Classical Hodgkin Lymphoma (LRCHL)
WHO definition:
LRCHL is a subtype of CHL with scattered HRS cells and a nodular or less often diffuse cellular background consisting of small lymphocytes and with an absence of neutrophils and eosinophils.
Epidemiology and clincal features:
LRCHL comprises 5% of CHL. The median age is similar to NLPHL (4th and 5th decades). There is male predominance (70%). Peripheral lymphadenopathy is more common. Mediastinal disease and bulky disease is uncommon. B symptoms are rare and most patients present with low stage disease. [19]
Morphology:
There are two patterns of lymph node involvement; a common nodular and a rare diffuse pattern. Nodules are closely packed with decreased T zones. Nodules may harbor germinal centres. Otherwise the nodules comprise of small lympho-cytes and HRS cells. A proportion of HRS cells may resemble popcorn or lacunar cells. HRS cells are present within the nodules. Eosinophils and neutrophils are rare. It has been noted that 30% of the cases reported as NLPHL in the past were actually LRCHL. It is sometimes very difficult to distinguish between NLPHL and LRCHL. Only immuophenotype solves the issue, with LRCHL depicting the Immunophenotype of CHL. LRCHL has been reported to coexist with MCCHL. In other instances, LRCHL has been seen followed by development of NSCHL.
Immunohistochemistry:
It is similar to that of CHL and is very important in differential diagnosis with NLPHL. EBV expression is more frequent than NSCHL but less frequent than MCCHL. [20]
Prognosis:
With modern therapy, prognosis is better than other CHL and similar to that of NLPHL. However relapses are more common in NLPHL than in LRCHL.
Lymphocyte Depleted Classical Hodgkin Lymphoma
WHO definition:
LDCHL is a diffuse subtype of CHL rich in HRS cells and depleted in non neoplastic lymphocytes.
Epidemiology and clinical features:
It is the rarest type of CHL (<1%). It more commonly involves males (60-75%). Median age ranges from 30-37 years. It is more common in developing countries and associated with HIV infection. LDCHL has predilection for retropeitoneal nodes, abdominal organs and bone marrow. [21] Comparatively it presents with more advanced stage and is more associated with B symptoms. Morphology: Morphology of LDCHL is highly variable, but the common feature is predominance of HRS cells inrelation to the background lymphocytes. In few cases HRS cells may show pleomorphism and in those cases, it is difficult to differentiate them from anaplastic form of nonHodgkin lymphoma. [22]
Immunophenotype:
Like other subtypes, Immunophenotype is same as that of other CHL. EBV is expressed in most HIV positive patients. [23]
Prognosis:
Prior to the advent of modern therapy, LDCHL used to follow aggressive course, but now the course is comparable to other CHL with similar stages. The prognosis is still poorer in some parts of Europe and in developing countries. Poor prognosis is seen in HIV positive cases.
Diagnosis of Hodgkin’s Lymphoma in Bone Marrow Trephine Biopsies
Bone marrow trephine biopsy is less often used for the primary diagnosis of Hodgkin lymphoma, because it is very rare for Hodgkin lymphoma to involve bone marrow in isolation. Bone marrow trephine biopsy is usually used in a previously diag-nosed case of Hodgkin lymphoma for staging purposes. Involvement of bone marrow means that the disease is dissem-inated and is a high stage disease.
The criteria are following:
In a previously diagnosed case of Hodgkin lymphoma, it is not necessary to find HRS cells in order to label the bone marrow being involved by Hodgkin lymphoma. In fact even presence of mononuclear cells with large nuclei and prominent eosino-philic nucleoli will serve the purpose. This can be further confirmed by immunostaining with CD15 and CD30.
In an unknown case presence of RS cells and mononuclear cells is mandatory. [24]
Microenvironment alone in the absence of RS cells although raises the suspicion of Hodgkin lymphoma, is not sufficient for diagnosis. [25]
Practical Points in Diagnosis of Hodgkin Lymphoma
The differential diagnosis of NLPHL includes T-cell/histiocyte-rich large B-cell lymphoma (THRLBCL) and LRCHL. The issue of differential diagnosis from THRLBCL rises in those cases of NLPHL where there is diffuse pattern of architecture efface-ment. [26] In these cases detection of one nodule showing the typical features of NLPHL is sufficient to exclude the primary diagnosis of THRLBCL. [3] In differential diagnosis from LRCHL, the search of remnant germinal centre is important. The later finding favors the diagnosis of LRCHL over NLPHL.
CHL cases rich in neoplastic cells may resemble anaplastic large cell lymphoma (ALCL). Identification as CHL requires positivity for PAX 5 and absence of EMA and ALK protein. Moreover the expression of EBV is more in favor of CHL. [15] The most difficult differential diagnosis is with large cell lymphoma with anaplastic morphology and CD30 positivity. There may be a biological overlap between this and CHL.
LDCHL with pleomorphic HRS cells may resemble anaplastic large cell lymphoma. In this case Positivity for PAX5 and D30 favors the diagnosis of LDCHL.
There are some lymphomas which have overlapping morphological and immunophenotypical features of CHL and diffuse large B-cell lymphomas. These lymphomas are now being classified as “B-cell lymphoma, unclassifiable, with features intermediate between diffuse large B-cell lymphoma and CHL”. [1]
Table 1: Differences in immunophenotype between NLPHL and CHL
Marker NLPHL CHL
CD30 - +
CD15 - +/-
CD45 + -
CD20 + -/+
CD79a + -/+
PAX5 + +
J chain +/- -
Ig +/- -
OCT2 + -/+
BOB1 + -
EMA +/- -
LMP1 - +/-
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