Imran N. Siddiqi

Myc and mTOR converge on a common node in protein synthesis control that confers synthetic lethality in Myc-driven cancers

Myc is one of the most commonly deregulated oncogenes in human cancer, yet therapies directly targeting Myc hyperactivation are not presently available in the clinic. The evolutionarily conserved function of Myc in modulating protein synthesis control is critical to the Myc oncogenic program. Indeed, enhancing the protein synthesis capacity of cancer cells directly contributes to their survival, proliferation, and genome instability. Therefore, inhibiting enhanced protein synthesis may represent a highly relevant strategy for the treatment of Myc-dependent human cancers. However, components of the translation machinery that can be exploited as therapeutic targets for Myc-driven cancers remain poorly defined. Here, we uncover a surprising and important functional link between Myc and mammalian target of rapamycin (mTOR)-dependent phosphorylation of eukaryotic translation initiation factor 4E binding protein-1 (4EBP1), a master regulator of protein synthesis control. Using a pharmacogenetic approach, we find that mTOR-dependent phosphorylation of 4EBP1 is required for cancer cell survival in Myc-dependent tumor initiation and maintenance. We further show that a clinical mTOR active site inhibitor, which is capable of blocking mTOR-dependent 4EBP1 phosphorylation, has remarkable therapeutic efficacy in Myc-driven hematological cancers. Additionally, we demonstrate the clinical implications of these results by delineating a significant link between Myc and mTOR-dependent phosphorylation of 4EBP1 and therapeutic response in human lymphomas. Together, these findings reveal that an important mTOR substrate is found hyperactivated downstream of Myc oncogenic activity to promote tumor survival and confers synthetic lethality, thereby revealing a unique therapeutic approach to render Myc druggable in the clinic.

Anaplastic large cell lymphoma occurring in association with breast implants: review of pathologic and immunohistochemical features in 103 cases.

Primary lymphomas of the breast are uncommon, and mostly of B-cell type. In the late 1990s, reports began to appear, primarily in the Pathology literature, of an apparently new category of breast lymphoma of T-cell type, having a particular association with silicone breast implants. This condition came to be recognized as implant-associated anaplastic large cell lymphoma. Appearing initially as individual case reports, the pathologic features were somewhat variable and the diagnosis was difficult. This review describes the pathologic and immunohistochemical features of implant-associated anaplastic large cell lymphoma of the breast drawn from a series of 103 cases. Recommendations are given for the management of removed implants, for the approach to differential diagnosis and the choice of initial immunohistochemical panels.

Histopathological findings in 29 lymph node biopsies with increased IgG4 plasma cells

IgG4-related sclerosing disease encompasses a family of disorders associated with increased numbers of IgG4 plasma cells and mass forming lesions in various tissues. Lymphadenopathy is a common finding, seen in up to 80% of cases. In the largest series of cases to date, we describe histologic, immunohistochemical, special stain and flow cytometric findings in 29 cases of enlarged lymph nodes with increased IgG4 plasma cells. Lymph node biopsies showed all resection specimens; no needle core biopsies of tissue were evaluated. Cases were considered to have increased numbers of IgG4 plasma cells using the histological criteria outlined by Cheuk and Chan (2010): IgG4 plasma cells >50 cells in a high-power field and >40% of IgG-positive plasma cells positive for IgG4. Additionally, increased intrafollicular plasma cells were a common finding. The lymph nodes showed a variety of reactive histological features including follicular hyperplasia, progressive transformation of germinal centers, interfollicular expansions, variable degrees of fibrosis, increased histiocytes and occasionally an appearance similar to that of plasma cell Castleman disease.

Autoimmune myelofibrosis: an update on morphologic features in 29 cases and review of the literature☆

Autoimmune myelofibrosis (AIMF) is a distinct clinicopathological entity associated with diffuse bone marrow fibrosis and a benign clinical course. Distinction from neoplastic etiologies of marrow fibrosis, particularly primary myelofibrosis, is imperative, but few studies have documented histopathologic features in a large series. We describe 29 patients with AIMF, defined as marrow reticulin fibrosis and lymphocytic infiltration in the context of an established autoimmune disorder (secondary AIMF) or autoantibodies without a defined disorder (primary AIMF). Excluded were cases with atypical megakaryocytes, dysplasia, basophilia, osteosclerosis, unexplained splenomegaly, or neoplasms associated with myelofibrosis (MF). All cases were stained for reticulin, CD3, and CD20, with a subset additionally stained for CD138, κ, λ, immunoglobulin G (IgG), and IgG4. Lymphoid aggregates, where present, were classified into T-cell and B-cell patterns of distribution. Most patients (93%) presented with cytopenias. Sixty-nine percent (n = 20) were considered secondary AIMF and the remainder primary AIMF (n = 9). Peripheral blood showed absent-to-rare blasts and teardrop erythrocytes and absence of eosinophilia or basophilia. Characteristic bone marrow findings included hypercellularity with erythroid and megakaryocytic hyperplasias, mild reticulin fibrosis, intrasinusoidal hematopoiesis, T-cell pattern in lymphoid aggregates, mild polytypic plasmacytosis, and absence of IgG4-positive plasma cells. Primary and secondary AIMF were pathologically indistinguishable, except for an increased incidence of granulocytic hyperplasia in primary AIMF. This series confirms and expands the utility of the original diagnostic criteria for AIMF. Recognizing the characteristic morphology of AIMF and its associated clinical and laboratory features distinguishes autoimmune from neoplastic causes of MF and guides further evaluation and management.

Pseudo-Pelger-Huët anomaly induced by medications: a clinicopathologic study in comparison with myelodysplastic syndrome-related pseudo-Pelger-Huët anomaly.

Pseudo-Pelger-Huët anomaly (PPHA) has been documented in association with transplant medications and other drugs. This iatrogenic neutrophilic dysplasia is reversible with cessation or adjustment of medications but is frequently confused with myelodysplastic syndrome (MDS) based on the conventional concept that PPHA is a marker for dysplasia. We investigated the clinicopathologic features in iatrogenic PPHA and compared them with MDS-related PPHA. The 13 cases studied included 5 bone marrow/stem cell transplantations, 3 solid organ transplantations, 1 autoimmune disease, 3 chronic lymphocytic leukemias, and 1 breast carcinoma. For 12 cases, there was follow-up evaluation, and all demonstrated at least transient normalization of neutrophilic segmentation. All 9 cases of MDS demonstrated at least 2 of the following pathologic abnormalities on bone marrow biopsy: hypercellularity (8/9), morphologic dysplasia (8/9), clonal cytogenetic abnormality (7/9), and increased blasts (3/9), whereas these abnormalities were typically absent in iatrogenic PPHA. Iatrogenic PPHA displayed a higher proportion of circulating PPHA cells than in MDS (mean, 47.4%; SD, 31.6% vs mean, 12.3%; SD, 9.8; P < .01). A diagnostic algorithm is proposed in which isolated PPHA is indicative of transient or benign PPHA unless proven otherwise.

Role of Histone Deacetylase Rpd3 in Regulating rRNA Gene Transcription and Nucleolar Structure in Yeast

ABSTRACT The 35S rRNA genes at the RDN1 locus in Saccharomyces cerevisiae can be transcribed by RNA polymerase (Pol) II in addition to Pol I, but Pol II transcription is usually silenced. The deletion of RRN9 encoding an essential subunit of the Pol I transcription factor, upstream activation factor, is known to abolish Pol I transcription and derepress Pol II transcription of rRNA genes, giving rise to polymerase switched (PSW) variants. We found that deletion of histone deacetylase gene RPD3 inhibits the appearance of PSW variants in rrn9 deletion mutants. This inhibition can be explained by the observed specific inhibition of Pol II transcription of rRNA genes by the rpd3Δ mutation. We propose that Rpd3 plays a role in the maintenance of an rRNA gene chromatin structure(s) that allows Pol II transcription of rRNA genes, which may explain the apparently paradoxical previous observation that rpd3 mutations increase, rather than decrease, silencing of reporter Pol II genes inserted in rRNA genes. We have additionally demonstrated that Rpd3 is not required for inhibition of Pol I transcription by rapamycin, supporting the model that Tor-dependent repression of the active form of rRNA genes during entry into stationary phase is Rpd3 independent.

p53 expression is a strong marker of inferior survival in de novo diffuse large B-cell lymphoma and may have enhanced negative effect with MYC coexpression: a single institutional clinicopathologic study.

OBJECTIVES To examine interactions among clinical factors and pathologic biomarkers in predicting the outcome of patients with diffuse large B-cell lymphoma (DLBCL) treated with rituximab-based immunochemotherapy. METHODS In 85 patients treated at a single institution, clinicopathologic variables were analyzed, including the International Prognostic Index (IPI); germinal/nongerminal center phenotype; MYC, p53, BCL2, Ki-67, and Epstein-Barr virus (EBV) expression; and MYC translocation status. RESULTS In univariate analysis, overall survival (OS) was worse for patients with high IPI scores, nongerminal center phenotype, high MYC and p53 expression by immunohistochemistry, and EBV positivity. In multivariable analysis, p53 expression was the strongest prognostic factor (P < .05) independent of IPI and cell of origin. A significant positive association between p53 and MYC expression was found. Moreover, coexpression of p53/MYC had an enhanced negative effect on OS independent of BCL2 expression. CONCLUSIONS Immunohistochemical assessment of p53, particularly in combination with MYC, could be useful in identifying a high-risk subgroup of DLBCL.

B-Cell Lymphoma With Hyaline Vascular Castleman Disease―Like Features: A Clinicopathologic Study

Hyaline vascular Castleman disease (HV-CD) is a localized benign mass characterized by follicular hyperplasia with atrophic germinal centers, mantle zone hyperplasia, hyaline deposits, and vascular proliferation. Before establishing a diagnosis of CD, several B-cell lymphomas (BCLs) must be considered, including follicular lymphoma (FL), mantle cell lymphoma (MCL), and nodal marginal zone lymphoma (NMZL). Conversely, BCLs with prominent atrophic germinal centers and hyaline vascular penetration may closely resemble HV-CD, leading to misdiagnosis. We report 6 cases of BCL with prominent HV-CD-like features, including FL (2 cases), MCL, NMZL (2 cases), and interfollicular large B-cell lymphoma. Histologically, all were initially considered to be HV-CD before additional tests revealed a neoplastic B-cell proliferation. We highlight the clinicopathologic features of these cases in comparison with cases diagnostic of HV-CD. In contrast with HV-CD, BCLs with HV-CD-like features are more likely to manifest clinically with systemic symptoms or generalized lymphadenopathy. Careful histopathologic examination, supported with immunohistochemical studies, flow cytometric immunophenotyping, and judicious use of cytogenetic and molecular analyses, allows identification of the masked neoplastic process. A multifaceted approach, integrating clinical, histologic, and ancillary tests, can help avoid this diagnostic pitfall.

20q– Clonality in a Case of Oral Sweet Syndrome and Myelodysplasia

We report the case of a patient with myelodysplasia who had Sweet syndrome of the oral cavity. An atypical myeloid immunophenotype was present in the gingival biopsy specimen and in a concurrent bone marrow specimen. Fluorescence in situ hybridization performed on the gingival biopsy specimen demonstrated the same del(20q) cytogenetic abnormality present in the bone marrow, confirming the presence of a clonally related myeloid proliferation in both tissues. This is the first reported case of Sweet syndrome and myelodysplasia in which the chromosomal abnormality was identified in the neutrophilic infiltrate, confirming the neutrophilic infiltrate to be clonally related to the underlying myeloid neoplasm.

Composite lymphoid neoplasm of B-cell and T-cell origins: a pathologic study of 14 cases ☆ ☆☆ ★

We retrospectively analyzed 14 composite lymphoma/lymphoid neoplasms (CL) of B-cell/T-cell origins. These consisted of a spectrum of T-cell neoplasms in combination with different B-cell lymphomas/leukemias, with peripheral T-cell lymphoma and diffuse large B-cell lymphoma encountered most frequently for each respective neoplastic lineage. Histopathologic evaluation demonstrated 6 patterns of neoplastic distribution, including zone, inverted zone, diffuse mixed, regional/nodular mixed, compartmental, and segmental distributions. Four of 9 cases studied were positive for Epstein-Barr virus, all with a mixed pattern, suggesting that this pattern may predict an Epstein-Barr virus association. None of 14 cases was considered CL at the initial histologic evaluation. Only 6 (46.2%) of 13 cases had coexisting B-cell/T-cell neoplasms highlighted by immunohistochemistry, and the other 7 (53.8%) cases had 1 or both of the neoplastic components hidden. Flow cytometry detected both neoplastic lineages in 4 (44%) but failed to detect a clonal B-cell population in 4 (44%) and missed neoplastic T cells in 1 (11.1%) of 9 cases. Molecular testing detected clonal rearrangement of IGH/K gene in 11 (84.6%) of 13 cases, and clonal rearrangement of the TCRG/B gene in 13 (92.9%) of 14 cases, including 8 with identical amplicons detected in separate samples. CLs of B-cell/T-cell origin are heterogeneous in subtype combination and topographic pattern, often with one of the components histologically occult. A multidisciplinary approach is emphasized to establish a definitive diagnosis in these challenging cases.