Anaplastic large-cell lymphoma
Anaplastic large-cell lymphoma refers to a group of non-Hodgkin lymphomas in which aberrant T cells proliferate uncontrollably. Considered as a single entity, ALCL is the most common type of peripheral lymphoma and represents ~10% of all peripheral lymphomas in children. The incidence of ALCL is estimated to be 0.25 cases per 100,000 people in the United States of America. There are four distinct types of anaplastic large-cell lymphomas that on microscopic examination share certain key histopathological features and tumor marker proteins. However, the four types have very different clinical presentations, gene abnormalities, prognoses, and/or treatments.
ALCL is defined based on microscopic histopathological examination of involved tissues which shows the presence of at least some ALCL-defining pleomorphic cells. These "hallmark" cells have abnormal kidney-shaped or horseshoe-shaped nuclei, prominent Golgi, and express the CD30 tumor marker protein on their surface membranes. In 2016, the World Health Organization separated ALCL into four types: ALK-positive ALCL, ALK-negative ALCL, primary cutaneous ALCL, and breast implant-associated ALCL. WHO defined BIA-ALCL as an ALCL type provisionally, i.e. subject to redefinition if future studies should support such a change.
ALK-positive and ALK-negative ALCL are aggressive systemic lymphomas. They are differentiated based on their expression of an abnormal ALK protein made by a somatic recombination in the ALK gene. ALK, i.e. anaplastic lymphoma kinase, is a protein product of the ALK gene located on chromosome 2. In ALK-positive ALCL, a portion of the ALK gene has merged with another site on the same or different chromosome to form a chimeric gene consisting of part of the new site and part of the ALK gene coding for ALK's activity. This chimeric gene overproduces a fusion protein with excessive ALK activity. ALK is a tyrosine kinase that activities PI3K/AKT/mTOR, Ras-activated ERKs, Janus kinase-activated STAT proteins, and other cell signaling pathways as well as the expression of various genes by epigenetic mechanisms. Activations of these signaling pathways and genes may stimulate cell growth, proliferation, survival, and/or other behaviors that promote malignancy. ALK-negative ALCL, while not involving ALK translocations, has, in a variable percentage of cases, various translocations, rearrangements, and mutations that may contribute to its development.
pcALCL and BIA-ALCL are far less aggressive lymphomas that tend to be localized to one or a very few sites. pcALCL presents as a single or, less commonly, multifocal skin papules or tumors that typically are limited to the dermis without infiltrating to the subcutaneous tissues or spreading to other sites. Its neoplastic cells may contain some gene translocations including, in very rare cases, ones with the ALK gene that are similar to those in ALK-positive ALCL. BIA-ALCL is caused by and develops around a breast implant. It typically presents many years after the surgical implantation as a deformation, textural change, and/or pain emanating in the area around implanted breast. In most cases, the disease is localized to the involved breast. BPI-ALCL is associated with occasional mutations in one or two genes but has not been reported to be associated with products of gene translocations or rearrangements.
ALK-positive anaplastic large-cell lymphoma
Signs and symptoms
ALK-positive ALCL occurs mostly but not exclusively in children and young adults and is slightly more common in males. Most individuals present with stage III or IV disease. They evidence systemic symptoms including B symptoms such as fever, night sweats, and weight loss in 75% of cases; lymph node enlargement including those in the mediastinum ; and lymphomatous lesions in the skin, bone, soft tissues, lung, and/or liver. Tumor cells are found in the bone marrow in up to 40% of the cases when immunohistochemical analysis is performed. Involvement of the central nervous system or a leukemia-like circulation of malignant cells in the blood occurs only very rarely. Most patients, including up to 90% of young children and adolescents, have circulating autoantibodies directed against the ALK fusion protein expressed by their tumor cells.Diagnosis
ALK-positive ALCL is diagnosed by histological and immunological examinations of involved tissues, typically lymph nodes. These tissues have lymphoma-like infiltrates that have variable numbers of ALCL "hallmark" cells, i.e. cells with kidney- or horseshoe-shaped nuclei that strongly express CD30 as detected by immunohistochemistry and an ALK fusion protein as detected by fluorescence in situ hybridization. These cells are scattered throughout the infiltrates. WHO classifies these infiltrates into 5 patterns: a common pattern consisting of large variably shaped cells with large nuclei that typically contain multiple nucleoli ; a small-cell pattern consisting of small to medium-sized neoplastic cells with clear cytoplasm and "hallmark" cells that are concentrated around small blood vessels ; a lymphohistiocytic pattern consisting of small neoplastic cells along with abundant histiocytes ; a Hodgkin's-like pattern in which the architecture resembles the nodular sclerosis pattern of Hodgkin lymphoma ; and a composite pattern consisting of two or more of the just described patterns. Detection of circulating autoantibody against ALK supports the diagnosis. Individuals with low levels of these autoantibodies are at an increase risk of relapsing after treatment.Gene and molecular abnormalities
In 80–85% of cases, the ALK detected in ALK-positive ALCL is a NPM1-ALK fusion protein. It is made by a fusion of NPM1 gene, which makes nucleophosmin 1, located on the long or "q" arm of chromosome 5 at position 35 with the ALK gene located on the short or "p" arm of chromosome 2 at position 23 to form a chimeric gene notated as. In 13% of cases ALK fuses with the TPM3 gene or in <1% of cases for each of the following genes: TFG, ATIC, CLTC, TPM4, MSN, RNF213, MYH9, or TRAF1. All of these fusion proteins are considered to act like NPMI-ALK in possessing high ALK activity that promotes the development and progression ALK-positive ALCL by activating the cell signaling pathways cited in the Introduction. 15% Of individuals with ALK-positive ALCL also have point mutations in the NOTCH1 gene. While most of these abnormalities are thought to be detrimental not all are. For example, DUSP22 gene rearrangements are associated with favorable outcomes in ALK-positive ALCL.Treatment and prognosis
A recommended induction therapy for ALK-positive ALCL in individuals with lesions containing more than 10 percent CD30-positive cells consists of brentuximab vedotin ; two chemotherapy drugs, cyclophosphamide and the anthracycline doxorubicin; and the corticosteroid, prednisone. This regimen gave a progression-free survival rate of 48.2 months in one study and overall survival rates of 70–90% at five years in other studies. For >60 year old and medically unfit individuals of any age, the standard CHOP regimen is used. For younger, medically fit individuals, the chemotherapeutic agent etoposide is added to the CHOP regimen. For patients with lesions that contain <10% CD30-positive neoplastic cells, brentuximab vedotin, which targets these cells, is not used. Rather, patients are treated with an anthracycline-based chemotherapy regimen. Patients >60 years or less medically fit are given cyclophosphamide, doxorubicin, vincristine, and prednisone while patients ≤60 years old are given CHOP plus etoposide or one of various other intensive chemotherapy regiments. The intensive chemotherapy regimens give 5 year overall survival rates of 70–93%. The role of radiation therapy for ALK-positive ALCL is unclear but has been used for patients who cannot tolerate or do not achieve complete responses to the drug regimens and to patients with organ-threatening or life-threatening tumorous infiltrates. The role of autologous or less preferably allogenic hematopoietic stem cell transplantation after achieving a complete remission following induction therapy is also unclear. Individuals with relapsed or refractory disease are treated with brentuximab vedotin if they did not receive the drug previously or had not received it in the previous 6 months. A small study reported overall response rates, complete response rates, and disease-free survival rates at 24 months of 63%, 45%, and 54%, respectively, using this regimen. Those who attain a complete response on this drug and can tolerate it are than treated with bone marrow transplantation. Finally, patients who fail or relapse on these treatments are given salvage therapy regimens that have been used for relapsed or refractory aggressive B cell malignancies such as GDP, DHAP, and ICE.Drugs that inhibit ALK activity such as crizotinib and alectinib have been successful in establishing complete and partial remissions in a limited number of patients with advanced, refractory ALK-positive ALCL. These and other drugs are undergoing clinical trials to determine there safety and effectiveness in treating ALK-positive ALCL.