CLL/SLL • Cytopenias or disease-related symptoms are now insufficient to make a diagnosis of CLL with <5 × 109/L PB CLL cells.

• Large/confluent and/or highly proliferative proliferation centers are adverse prognostic indicators.

• Mutations of potential clinical relevance, such as TP53, NOTCH1, SF3B1, ATM, and BIRC3, have been recognized.

Monoclonal B-cell lymphocytosis • Must distinguish low-count from high-count MBL.

• A lymph node equivalent of MBL exists.

Hairy cell leukemia • BRAF V600E mutations in vast majority of cases with MAP2K1 mutations in most cases that use IGHV4-34 and lack BRAF mutation.

Lymphoplasmacytic lymphoma (LPL) • MYD88 L265P mutation in vast majority of cases impacting diagnostic criteria even though finding is not specific for LPL.

• IgM MGUS is more closely related to LPL and other B-cell lymphomas than to myeloma.

Follicular lymphoma (FL) • Mutational landscape better understood but clinical impact remains to be determined.

In situ follicular neoplasia • New name for in situ follicular lymphoma reflects low risk of progression to lymphoma.

Pediatric-type FL • A localized clonal proliferation with excellent prognosis; conservative therapeutic approach may be sufficient.

• Occurs in children and young adults, rarely in older individuals.

Large B-cell lymphoma with IRF4 rearrangement • New provisional entity to distinguish from pediatric-type FL and other DLBCL.

• Localized disease, often involves cervical lymph nodes or Waldeyer ring.

Duodenal-type FL • Localized process with low risk for dissemination.

Predominantly diffuse FL with 1p36 deletion • Accounts for some cases of diffuse FL, lacks BCL2 rearrangement; presents as localized mass, often inguinal.

Mantle cell lymphoma (MCL) • Two MCL subtypes recognized with different clinicopathological manifestations and molecular pathogenetic pathways: one largely with unmutated/minimally mutated IGHV and mostly SOX11+ and the other largely with mutated IGHV and mostly SOX11− (indolent leukemic nonnodal MCL with PB, bone marrow (BM), ±splenic involvement, may become more aggressive).

• Mutations of potential clinical importance, such as TP53, NOTCH 1/2, recognized in small proportion of cases.

• CCND2 rearrangements in approximately half of cyclin D1− MCL.

In situ mantle cell neoplasia • New name for in situ MCL, reflecting low clinical risk.

Diffuse large B-cell lymphoma, NOS • Distinction of GCB vs ABC/non-GC type required with use of immunohistochemical algorithm acceptable, may affect therapy.

• Coexpression of MYC and BCL2 considered new prognostic marker (double-expressor lymphoma).

• Mutational landscape better understood but clinical impact remains to be determined.

EBV+ DLBCL, NOS • This term replaces EBV+ DLBCL of the elderly because it may occur in younger patients.

• Does not include EBV+ B-cell lymphomas that can be given a more specific diagnosis.

EBV+ mucocutaneous ulcer • Newly recognized entity associated with iatrogenic immunosuppression or age-related immunosenescence.

Burkitt lymphoma • TCF3 or ID3 mutations in up to ∼70% of cases.

Burkitt-like lymphoma with 11q aberration • New provisional entity that closely resembles Burkitt lymphoma but lacks MYC rearrangement and has some other distinctive features.

High-grade B-cell lymphoma, with MYC and BCL2 and/or BCL6 translocations • New category for all “double-/triple-hit” lymphomas other than FL or lymphoblastic lymphomas.

High-grade B-cell lymphoma, NOS • Together with the new category for the “double-/triple-hit” lymphomas, replaces the 2008 category of B-cell lymphoma, unclassifiable, with features intermediate between DLBCL and Burkitt lymphoma (BCLU).

• Includes blastoid-appearing large B-cell lymphomas and cases lacking MYC and BCL2 or BCL6 translocations that would formerly have been called BCLU.

T-cell large granular lymphocyte leukemia • New subtypes recognized with clinicopathologic associations.

• STAT3 and STAT5B mutations in a subset, latter associated with more clinically aggressive disease.

Systemic EBV+ T-cell lymphoma of childhood • Name changed from lymphoproliferative disorder to lymphoma due to its fulminant clinical course and desire to clearly distinguish it from chronic active EBV infection.

Hydroa vacciniforme–like lymphoproliferative disorder • Name changed from lymphoma to lymphoproliferative disorder due to its relationship with chronic active EBV infection and a spectrum in terms of its clinical course.

Enteropathy-associated T-cell lymphoma (EATL) • Diagnosis only to be used for cases formerly known as type I EATL, typically associated with celiac disease.

Monomorphic epitheliotropic intestinal T-cell lymphoma • Formerly type II EATL; segregated from type I EATL and given a new name due to its distinctive nature and lack of association with celiac disease.

Indolent T-cell lymphoproliferative disorder of the GI tract • New indolent provisional entity with superficial monoclonal intestinal T-cell infiltrate, some cases show progression.

Lymphomatoid papulosis • New subtypes described with similar clinical behavior but atypical histologic/immunophenotypic features.

Primary cutaneous γ δ T-cell lymphoma • Important to exclude other cutaneous T-cell lymphomas/lymphoproliferative disorders that may also be derived from γ δ T cells such as mycosis fungoides or lymphomatoid papulosis.

Primary cutaneous acral CD8+ T-cell lymphoma • New indolent provisional entity, originally described as originating in the ear.

Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder • No longer to be diagnosed as an overt lymphoma due to limited clinical risk, localized disease, and similarity to clonal drug reactions.

• Remains a provisional entity.

Peripheral T-cell lymphoma (PTCL), NOS • Subsets based on phenotype and molecular abnormalities being recognized that may have clinical implications but are mostly not a part of routine practice at this time.

Nodal T-cell lymphomas with T-follicular helper (TFH) phenotype • An umbrella category created to highlight the spectrum of nodal lymphomas with a TFH phenotype including angioimmunoblastic T-cell lymphoma, follicular T-cell lymphoma, and other nodal PTCL with a TFH phenotype (specific diagnoses to be used due to clinicopathologic differences).

• Overlapping recurrent molecular/cytogenetic abnormalities recognized that potentially could impact therapy.

ALK− anaplastic large-cell lymphoma • Now a definite entity that includes cytogenetic subsets that appear to have prognostic implications (eg, 6p25 rearrangments at IRF4/DUSP22 locus).

Breast implant–associated anaplastic large cell lymphoma • New provisional entity distinguished from other ALK− ALCL; noninvasive disease associated with excellent outcome.

Nodular lymphocyte–predominant Hodgkin lymphoma • Variant growth patterns, if present, should be noted in diagnostic report, due to their clinicopathologic associations.

• Cases associated with synchronous or subsequent sites that are indistinguishable from T-cell histiocyte-rich large B-cell lymphoma (THRLBCL) without a nodular component should be designated THRLBCL-like transformation.

Lymphocyte-rich classical Hodgkin lymphoma • Features recognized that are intermediate between NLPHL and other types of classical Hodgkin lymphoma.

Erdheim-Chester disease • Should be distinguished from other members of the juvenile xanthogranuloma family; often associated with BRAF mutations.