Faith C. S. Ho

Report of the Workshop on Nasal and Related Extranodal Angiocentric T/Natural Killer Cell Lymphomas. Definitions, differential diagnosis, and epidemiology

A workshop jointly sponsored by the University of Hong Kong and the Society for Hematopathology explored the definition, differential diagnosis, and epidemiology of angiocentric lymphomas presenting in the nose and other extranodal sites. The participants concluded that nasal T/natural killer (NK) cell lymphoma is a distinct clinicopathologic entity highly associated with Epstein-Barr virus (EBV). In situ hybridization for EBV an be very valuable in early diagnosis, especially if tissue is sparse. The cytologic spectrum is broad, ranging from small or medium-sized cells to large transformed cells. Histologic progression often occurs with time. Necrosis is nearly always present, and angioinvasion by tumor cells is seen in most cases. Nasal T/NK cell lymphoma has a characteristic immunophenotype: CD2-positive, CD56-positive, but usually negative for surface CD3. Cytoplasmic CD3 can be detected in paraffin sections. Clonal T-cell receptor gene rearrangement is not found. Tumors with an identical phenotype and genotype occur in other extranodal sites, most commonly in the skin, subcutis, and gastrointestinal tract, and should be referred to as nasal-type T/NK cell lymphomas. The differential diagnosis includes lymphomatoid granulomatosis, blastic or monomorphic NK cell lymphoma/leukemia, CD56-positive peripheral T-cell lymphoma, and enteropathy-associated T-cell lymphoma.

Polymorphic reticulosis and conventional lymphomas of the nose and upper aerodigestive tract: A clinicopathologic study of 70 cases, and immunophenotypic studies of 16 cases

Seventy patients with malignant lymphomas, including the entity known as polymorphic reticulosis (PR), involving the nose, nasal sinuses, nasopharynx, oropharynx (excluding tonsil), and larynx were studied. There were 26 cases of PR, 19 cases of lymphoma with features of PR (ML[PR]) and 25 cases of conventional lymphomas. Fourteen of the 25 conventional lymphomas were due to dissemination from distant sites. For all histologic types of primary lymphoma, the presenting symptoms were similar, and the nasal cavity was more commonly involved than the nasopharynx. Patients with PR were younger, had a higher male:female ratio, and had a better overall survival rate than patients with conventional lymphomas. Cryostat section immunohistochemistry performed on 17 samples from 16 patients showed only one B lymphoma out of 11 primary lesions; the other 10 cases and three recurrent tumors at distant sites showed phenotypic markers of T lymphocytes and natural killer cells. All three secondary tumors were of B-cell type. Of eight patients with sequential biopsies, progression to a more malignant histopathologic type was found in six. In the PR and ML[PR] biopsies, angiocentricity was detected in 11%, and angioinvasion in 22%. We could not confirm identity of PR with other angiocentric immunoproliferative lesions.

Nasal NK- and T-cell lymphomas share the same type of Epstein-Barr virus latency as nasopharyngeal carcinoma and Hodgkin's disease

Nasal T/NK‐cell lymphomas can be further separated into those of natural killer (NK) cell lineage or of T‐cell lineage, with differences in cellular phenotype, T‐cell receptor (TcR) gene rearrangement and TcR transcript expression. Both NK‐ and T‐cell subtypes are closely associated with Epstein‐Barr virus (EBV). In this study, EBV gene expression was determined in 23 cases of nasal lymphoma (NL) by in situ hybridisation (ISH), reverse transcriptase‐polymerase chain reaction (RT‐PCR) and immunohistochemistry (IH). Of the 23 cases, 19 were classified as NK‐cell and 4 as T‐cell tumours. ISH for EBV‐encoded small non‐polyadenylated RNAs showed that all cases, whether NK or T, harboured EBV in virtually all tumour cells. RT‐PCR demonstrated that NL of both subtypes expressed EBNAI of the QUK splice pattern, the latent membrane proteins, LMPI and 2 and the BamHI A rightward transcripts in the absence of EBNA2 mRNAs, compatible with the latency type II pattern. In addition, analysis of EBV protein expression by IH revealed a heterogeneous pattern of EBV gene expression at the single‐cell level consisting of both LMPI+ and LMPI‐ tumour cells, suggesting a mixture of latency I and II. Although 2 early lytic transcripts, BZLFI and BHRFI, were also detected in 13 and 10 cases, respectively, the lack of ZEBRA staining in any case indicates that these lytic transcripts are most likely expressed by rare cells in the biopsies entering lytic cycle. The viral transcriptional pattern similar to that of nasopharyngeal carcinoma and Hodgkins disease suggests that EBV can exploit common regulatory mechanisms for gene transcription in diverse host cell types. Down‐regulation of immunogenic proteins (EBNA2‐EBNA6) in nasal lymphoma may enable tumour cells to evade host cytotoxic T‐cell surveillance.

Nasal T/natural killer (NK)-cell lymphomas are derived from Epstein-Barr virus–infected cytotoxic lymphocytes of both NK- and T-cell lineage

The cellular nature of nasal T/natural killer (NK)‐cell lymphomas (NLs) remains controversial. It is still debatable whether these represent T‐cell lymphomas with extensive loss of surface antigens or are, in fact, true NK‐cell lymphomas. They are associated closely with Epstein‐Barr virus (EBV), to the extent that EBV‐encoded small non‐polyadenylated RNAs (EBER) expression can be used as a marker for the neoplastic cells. The cell lineage of this group of lymphomas was examined further by correlating immunophenotype, genotype and EBV status with the expression of cytotoxic granule‐associated proteins, perforin and T‐cell intracellular antigen‐1 (TIA‐1) in 13 cases of NL. Combined immunophenotypic and gene rearrangement analyses demonstrated that NLs can be identified clearly as either NK‐cell or T‐cell tumours. Nasal NK‐cell lymphomas lacked clonal rearrangement of both T‐cell receptor (TCR) γ and immunogloulin heavy chain (IgH) genes and were either CD3(Leu4)−CD56+ (8 cases) or CD3(Leu4)+CD56+ (2 cases), whereas nasal T‐cell lymphomas had rearranged TCRγ and germ‐line IgH genes and were either CD3(Leu4)+CD56+ (2 cases) or CD3(Leu4)+CD56− (1 case). Immunohistochemical (IH) studies showed that both perforin and TIA‐1 were expressed universally in NL, irrespective of NK‐ or T‐cell lineage. Dual labelling of TIA‐1 by IH and EBER by in situ hybridisation demonstrated that the granule proteins were expressed predominantly by the EBER+ tumour cells. Our results indicate that NLs are derived from EBV‐infected cytotoxic lymphocytes of both NK‐ and T‐cell lineage. We postulate that cytotoxic lymphocytes generated during the cellular immune response to EBV infection or re‐activation at the nasal region themselves may become targets for EBV infection and subsequent transformation. Int. J. Cancer 73:332–338, 1997.

HUMAN COLOSTRAL AND BREAST MILK CELLS A Light and Electron Microscopic Study

Abstract. Colostrum and breast milk samples were obtained from 74 women, 18 of whom gave sequential samples. The mean total leukocyte count in colostrum was 3190 cells/mm3. Proportions of macrophages, polymorphs and lymphocytes varied widely; macrophages usually predominated. Serial sampling showed (1) a small fall in total counts through delivery, (2) a fall in total counts and the proportion of PMNs at the onset of lactation, (3) after 1 to 2 weeks of lactation the appearance of cytoplasmic fragments together with epithelial cells which later constituted the main cell type. It was estimated that the total number of leukocytes available to the neonate remained approximately constant during the first 2 weeks of lactation and fell thereafter. Functionally, morphologically and histochemically macrophages in colostrum and breast milk resembled macrophages elsewhere. Their ultrastructure was characterised by filiform surface projections, numerous endocytic vacuoles and lipid droplets in the cytoplasm.

Evaluation of a histogenetic classification for thymic epithelial tumours

We reviewed 87 thymic epithelial tumours from Chinese patients and typed them according to the Marino and Müller‐Hermelink classification as updated by Kirschner and Müller‐Hermelink in 1989. Related categories were grouped for statistical analyses; group 1, medullary thymoma and mixed thymoma; group 2, cortical predominant thymoma; group 3, cortical thymoma and well‐differentiated thymic carcinoma; group 4, other thymic carcinomas; and group 5, unclassified. Group 3 tumours were more frequently associated with the myasthenia gravis syndrome compared with group 1 tumours (P=0.001). They also presented at a more advanced stage. Groups 1 and 2 showed an excellent prognosis (100% survival at 10 years). The 10‐year survival for groups 3 and 4 patients was 40% and 30% respectively. Pure medullary thymoma made up a higher proportion of our cases (10.3%) than those of a similar Caucasian study (5.3%). The eight thymic carcinomas (group 4) included two thymic lymphoepitheliomas. We conclude that the histogenetic classification evaluated shows a clear correlation with prognosis and clinical features, even when tested on separate geographic groups, where pathogenetic factors may be different. A common approach to classification of thymic epithelial tumours would greatly facilitate future studies on these possible differences.

Frequent detection of Epstein–Barr virus‐infected B cells in peripheral T‐cell lymphomas

Although Epstein–Barr virus (EBV) positivity has been described in peripheral T‐cell lymphomas (PTCLs) in Chinese patients, the cellular lineage of EBV‐harbouring cells is unknown. Forty‐four cases of PTCL were therefore studied by in situhybridization (ISH) for EBV‐encoded small non‐polyadenylated RNA 1 and 2 (EBER), and the lineage of the EBER+ cells was determined by double labelling. The findings were further correlated with the clonality of EBV and the genotype of these EBER+ tumours. The results for the detection of EBV by ISH show that 23 of the 44 cases were EBER+. In 5/23 of the EBER+ cases, EBER was found in around 50 per cent of atypical cells and in 18/23 cases, EBER was found in a subpopulation of atypical cells. Amongst the EBER+ cases, all 15 tested showed clonal T‐cell receptor gene rearrangement by Southern blot hybridization. Double labelling was successfully done in 11 EBER+ cases, and by comparison, EBER+/CD20+ B cells outnumbered the EBER+/CD3+ T cells in all these cases. EBV clonality analysis revealed that EBV was monoclonal in six EBER+ cases and biclonal in three cases. With the predominance of EBV+ B cells over EBV+ neoplastic T cells being observed in most of these cases, it is possible that the EBV‐infected clonal population may be of B‐cell lineage. This was supported in some cases where a faint clonal band was seen over a background smear in the gene rearrangement study of immunoglobulin heavy chain gene by polymerase chain reaction (PCR), indicating a minor B‐cell clone. It is concluded that in EBV+ PTCL, EBV is preferentially localized in B cells rather than neoplastic T cells. The neoplastic T cells may support the clonal proliferation of a subpopulation of EBV+ B cells in PTCLs.

Differences in T-cell-receptor gene rearrangement and transcription in nasal lymphomas of natural killer and T-cell types : Implications on cellular origin

Although nasal lymphomas showing midfacial destructive lesions had been classified as T-cell lymphomas, their exact cellular origin is still unclear. Although they usually express a restricted number of T-cell-related antigens, namely, CD2, CD43, and CD45RO, other pan-T or subset-T-lineage antigens, such as CD3 (membrane), CD5, CD4, CD8, and CD7, are frequently absent. Conversely, they often express a natural killer (NK) cell-associated antigen, CD56, but lack other mature NK markets. To study their cellular origin further, the authors analyzed T-cell receptor (TCR) gene transcription in three cases of nasal lymphomas and correlated the findings with the phenotype and gene rearrangement data. Two cases of nasal lymphomas with CD2+CD3(Leu4)-CD19-CD56+ phenotype were shown to express truncated 1.0-kb Tbeta and multiple unrearranged Tdelta transcripts with germline TCR beta, gamma, delta, and immunoglobulin heavy-chain joining region (JH) genes, consistent with NK cell lineage. In contrast, one case of nasal lymphoma with CD2+CD3(Leu4)+CD8+CD19-CD56+ phenotype expressed full-length Talpha, Tbeta, and Tgamma transcripts rearranged TCR beta, gamma, and deleted TCR delta genes, indicating T-lineage, These results support the view that nasal lymphomas can separated into NK-cell and T-cell neoplasms, based on differences genotypic characteristics. The possibility of these tumors being derived from a putative common precursor cell merits further investigation.

Pigmented carcinoid tumour of the thymus

An asymptomatic thymic tumour, classified as a carcinoid tumour on the basis of its light and electron‐microscopic appearances, is described. This tumour was atypical in having foci of melanin pigmentation, the pigment being contained in dendritic melanocytes and melanophages. We suggest that the pigmented cells are not neoplastic and represent latent thymic melanoblasts stimulated in some way by the carcinoid tumour. Alternative explanations are discussed.

Immunohistological subtypes of non-Hodgkin's lymphoma in Hong Kong Chinese.

&NA; Summary One hundred and four unselected cases of non‐Hodgkins lymphoma (NHL) in adult Chinese patients in Hong Kong were typed, using monoclonal and conventional antibodies, by immunoenzymatic labelling methods on cryostat sections or cell smears. The total included 69 cases (66%) of B‐cell and 26 (25%) of T‐cell tumours. The diffuse large cell (centroblastic or immunoblastic) types formed the largest proportion (44.9%) of B lymphomas. Of 26 cases of T‐cell lymphoma 25 were of peripheral type; of these 25, the most frequent subtype (42.3%) was the immunoblastic lymphadenopathy‐like lesion. Although there were 9 pleomorphic T‐cell lymphomas, none of the patients presented with the adult T‐cell leukemia/lymphoma syndrome. The incidence of T‐cell lymphomas in our population is not markedly higher than that of western countries, but there are some interesting differences in the types of T‐cell lymphomas that are commonly seen.