Anaplastic large cell lymphoma (ALCL) is a well-recognized clinicopathological entity that comprises about 2% of all non-Hodgkin Lymphomas (NHLs) in adults and about 13% of NHLs in children [1]. Initially defined by Stein et al. [2] in 1985 as anaplastic large cell Ki-1-positive (since renamed as CD30) lymphomas, ALCL is an aggressive form of NHL, which involves large pleomorphic lymphoid cells and cohesive growth patterns with a strong uniform expression of antigen CD30. Such tumors have histopathological similarity with typical Hodgkin's lymphoma (CHL), especially regarding morphology and immunophenotype. Another distinguishing characteristic of ALCL is that it tends to infiltrate lymph node sinuses, thus helping in its histopathological identification [2]. ALCL was initially classified by the Keil classification and later incorporated into the Revised European–American Lymphoma (REAL) classification and subsequently recognized formally in 2001 by the WHO classification of hematopoietic and lymphoid tissues [2]. It was recognized as of T-cell origin, which was confirmed by T-cell receptor (TCR) gene rearrangement and immunophenotypic studies. These studies have demonstrated expression or loss of T cell markers such as CD3 and CD5 [2]. Thus, it was classified as a unique subtype of Peripheral T-cell lymphoma (PTCL). The common characteristic of ALCL is that all cases express diffuse and strong CD30 positivity, although differentiation can be given in terms of clinical presentation, morphology, and molecular profile. The latest update of the lymphoma taxonomy (2016) by the WHO acknowledges four major ALCL, including systemic ALK-positive (ALK+ ALCL), systemic ALK-negative (ALK– ALCL), primary cutaneous ALCL (pc-ALCL), and breast implant-associated ALCL (BI-ALCL)[2]. These subtypes exhibit distinct histomorphological, immunohistochemical, and molecular characteristics affecting their clinical behaviour and prognosis. In ALK-positive ALCL, which mainly affects the younger patients, translocation of the ALK gene on chromosome 2p23 leads to the expression of the ALK fusion protein. The subtype has a better prognosis than ALK-negative ALCL, which tends to impact individuals who are aged and have a more aggressive clinical course in most cases [3]. The morphology of ALCL shows different patterns, which include common, small cell, and lymphohistocytic variants [2]. Small cell and lymphohistiocytic subtypes are often associated with leukemic manifestation and have a worse prognosis compared to the classic subtype. Histopathologically, the hallmark cells are large, pleomorphic cells with horseshoe-shaped or kidney-shaped nuclei and have abundant cytoplasm. These cells are characteristically seen in all ALCL subtypes [4]. Epidemiological studies have indicated that the general rate of incidence of ALCL among Asian people is quite low compared to Western populations [5, 6]. But there is a paucity of data on the Indian subcontinent. Since the clinicopathological profile and prognosis may vary between the subtypes of ALCL, local studies are needed to gain a more detailed insight into the disease patterns, presentation, and outcome in various populations. Since there is a paucity of data on clinicopathological and IHC features of ALCL from Indian studies, our study will share important data for understanding the disease in this population. With this background, we designed the present study to evaluate the clinicopathological characteristics and histopathological findings, including the immunohistochemical profile of ALCL reported in our tertiary care hospital

This retrospective observational study was conducted in the Department of Pathology at St. John’s Medical College and Hospital, Bengaluru, Karnataka. Institutional Ethical approval was obtained for the study. All cases that were histopathologically diagnosed as Anaplastic Large Cell Lymphoma (ALCL) received in the department during this period were included. All the relevant records, which included clinical observations and pathological data, were collected from the hospital record section and analyzed. Inclusion criteria 1. Cases of anaplastic large cell lymphoma where standard IHC was done 2. Those cases were reported during the specified duration of the study(1st January 2008- 30th June 2022). 3. Males and females 4. All the relevant complete clinical and histopathological details are available. Exclusion criteria 1. Breast implant-associated ALCL was excluded 2. Cases with a lack of clinical information 3. Insufficient tissue or no blocks available Sample size calculation: To estimate the prevalence of ALK-positive cases with an absolute precision of 15% and a 95% confidence interval, the required minimum sample size was 37 ALCL patients. Histopathological Evaluation: Formalin-fixed paraffin-embedded tissues stained with Hematoxylin and Eosin (H&E) were studied. Morphological analysis was done to evaluate the morphological subtype, presence of “Hallmark” cells, Lymph node architecture, and sinusoidal involvement. These cases were classified using the World Health Organization (WHO) classification of the lymphoid neoplasms. Immunohistochemistry (IHC): IHC markers studied were CD30, ALK, CD3, CD15, CD20, EMA, and LCA. Interpretation of the expression pattern and intensity was performed in a semi-qualitative manner. According to the ALK expression, the cases were categorized into ALK-positive or ALK-negative ALCL. Statistical analysis: All the available data were segregated, refined, and uploaded to an MS Excel spreadsheet and analyzed by SPSS version 26 in Windows format. The continuous variables were represented as mean, standard deviation, frequency, and percentages. The categorical variables were calculated by Student's t-test for comparing means of two groups and the square test to calculate differences between two groups.

Table 4: Immunohistochemical (IHC) profile of ALCL cases (N=39) IHC Marker Result Frequency (n) Percentage (%) ALK Status Positive 32 82.1 Negative 7 17.9 CD30 Positive 39 100 Negative 0 0.0 LCA(CD45) Positive 39 100 Negative 0 0.0 CD3 Positive 27 69.2 Negative 12 30.8 EMA Positive 18 46.2 Negative 21 53.8 CD15 Positive 0 0.0 Negative 39 100 CD20 Positive 0 0.0 Negative 39 100 Table 5 shows the details of the ALK staining pattern in (ALK-positive) cases and the distribution of extranodal involvement. Out of 32 of the ALK-positive cases, the most common staining pattern was the cytoplasmic and nuclear (C+N), present in 53.1% of the cases, followed by the pure cytoplasmic (37.5%) and nuclear-only (9.4%) stainings. These ALK translocations have been implicated as having diagnostic and prognostic significance due to their variation in ALK gene translocation partners. Of the 13 extranodal sites involved, the most common sites included skin (23%), lung (15.4%), soft tissue (15.4%), bone marrow (15.4%), and mediastinal lymph nodes (15.4%), and primary cutaneous ALCL and bone involvement were each observed in 7.7%. There was no evidence of leukemic involvement. The extranodal spread and the variable ALK staining observed support the clinical heterogeneity of ALCL presentation, with many organs involved. Table 5: ALK Staining Patterns and Spectrum of Extranodal Involvement A: ALK Staining Pattern in ALK-positive cases (n=32) Frequency (n) Percentage (%) Cytoplasmic and Nuclear (C+N) 17 53.1 Cytoplasmic (C) 12 37.5 Nuclear (N) 3 9.4 B: Extranodal Sites Involved (n=13 cases had extranodal disease) Secondary Skin Involvement 3 23.0 Lung 2 15.4 Soft Tissues 2 15.4 Bone Marrow 2 15.4 Mediastinal Lymphadenopathy 2 15.4 Primary Skin Involvement (PC-ALCL) 1 7.7 Bone 1 7.7 Leukemic Involvement 0 0.0 Photomicrographs showing histopathological and immunohistochemical features of some important cases of Anaplastic Large Cell Lymphoma (ALCL) in our study are given in Figure 1.

Anaplastic large cell lymphoma (ALCL) is a unique clinicopathological entity among non-Hodgkin lymphomas (NHL) that has been redefined considerably since its initial description. Stein et al first described it in 1985 as a subset of NHL with large anaplastic lymphoid cells expressing CD30 with cohesive growth and sinusoidal invasion, first described as Ki-1 lymphoma. Later, it was classified as ALCL in the World Health Organization (WHO) scheme of lymphoid neoplasms [7]. ALCL accounts for roughly 2% of all NHLs and around 20 % of peripheral T-cell lymphomas in North America, whereas the incidence was found to be lower in Europe and Asia [8]. ALCL is a T-cell lymphoma characterized by strong and diffuse CD30 positivity and is characterized by the presence of "hallmark cells", which are large pleomorphic cells with horseshoe- or kidney-shaped nuclei with a clear zone surrounding the nucleus [9, 10]. The more recent WHO 2017 classification recognises four entities within the scope of ALCL: ALK-positive ALCL, ALK-negative ALCL, primary cutaneous ALCL (pc-ALCL), and breast implant-associated ALCL. These variants vary in their morphology, immunohistochemistry, and clinical behavior [11]. ALK-positive ALCL typically shows ALK gene rearrangements, most often the t(2;5) (p23; q35) translocation, conferring a better prognosis than does ALK-negative ALCL [12]. Histopathologically, CD30 expression is diffuse and strong with membranous and paranuclear (Golgi) staining. The neoplastic cells often efface the lymph node architecture and show sinusoidal infiltrations. The presence of characteristic cells known as hallmark cells and characteristic patterns of growth are features that allow ALCL to be distinguished from other large-cell lymphomas [13, 14]. Following the identification of the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion gene, studies defined ALK-positive ALCL as a biological entity. Savage et al have shown that ALK-negative ALCL is significantly different from peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), both in terms of immunophenotype and clinical outcome [15]. ALK-positive ALCL occurs in younger patients and has a good prognosis with a 5-year overall survival (OS) around 70 % in comparison to ~49 % in ALK-negative cases [16]. In the present study of biopsy-proven cases of ALCL (n=39), demographic, morphological, and immunophenotypic characteristics were examined in order to describe the spectrum of the disease in a tertiary care setting. The mean age was 27.6 years; thus, ALCL affects mainly younger people, with a definite male predominance (M: F = 2.9:1). Similar demographic trends have been recorded in previous series [13, 17]. The majority of cases were presented with nodal involvement (66.7 %), with combined nodal and extranodal disease occurring in one-fourth of cases. Hepatosplenomegaly was found in 35.9 % of the patients, in accord with previous reports of frequent systemic dissemination [17, 18]. Histopathological evaluation showed that the prevalent or classical morphological pattern was classical (82.1 %), followed by Hodgkin-like and small-cell variants. All of these features showed universal presence of “hallmark cells” and frequent lymph node effacement with sinus involvement (75 %), confirming the diagnostic importance of these features [14, 17]. On immunohistochemical evaluation, CD30 and LCA (CD45) were uniformly positive, as is expected in ALCL. ALK expression was observed in 82.1% of cases, indicating that the disease is predominantly ALK-positive in our cohort. CD3 was positive in 69.2%, and EMA positivity was observed in 46.2% of the cases. CD15 and CD20 were negative in all cases, thus differentiating ALCL from classical Hodgkin lymphoma and B-cell lymphomas, respectively. These results are similar to those of Abbasi et al. [17] and Lakshmaiah et al. [18]. Among ALK-positive cases, the most frequent staining pattern was combined cytoplasmic and nuclear (53.1 %), followed by purely cytoplasmic (37.5 %) and nuclear (9.4 %) patterns. The cytoplasmic and nuclear staining corresponds to NPM-ALK fusion resulting from the classic t(2;5) (p23;q35) translocation [13, 19]. Extranodal disease was present in 33% of cases, most often involving skin, lung, soft tissue, and bone marrow, which is similar to previous studies [18, 19]. In summary, the present study reaffirms that ALCL, especially ALK-positive ALCL, mainly occurs in younger males, has diffuse and strong CD30 expression, and has a typical morphology as described in the literature. The combination of clinical, histopathological, and IHC parameters, nonetheless, is still of paramount importance for correct diagnosis and subtyping. The results add to the sparse regional data on ALCL and also support the available literature on the clinicopathological spectrum and IHC profile of ALCL in the Indian population.

In this study, most patients diagnosed with Anaplastic Large Cell Lymphoma (ALCL) were younger than 20 years, with a male predominance. Fever and nodal involvement were the most frequent clinical presentations, while the skin was the most common extranodal site. Elevated serum LDH levels were observed in the majority. Histologically, the common pattern was predominant, followed by the Hodgkin-like variant, with “hallmark cells” seen in all cases. Lymph node effacement and sinusoidal involvement were frequent. Immunohistochemically, all cases were CD30 and CD45 positive, over half were ALK positive, and one-third showed CD3 loss. CD15 and CD20 were consistently negative.

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