Richter transformation: uncommon, serious, and recognisable¶

13.1 Incidence in perspective¶

Richter transformation (RT) means CLL turning into an aggressive lymphoma. About 90% are of the DLBCL type and 10% Hodgkin type (VP8.2 §17.2).

Population	Risk
Across the whole course of CLL (EHA)	2–10%
Swedish guideline estimate	0.5–1% per year
Danish nationwide cohort, 2008–2016	5-year cumulative incidence 2.8% from diagnosis; half of cases arose in untreated patients
Mayo Clinic, newly diagnosed	2.3% overall: about 0.5% per year, doubling to 1% per year after treatment
Norway	4.7 per 1,000 person-years
Real-world ibrutinib cohort, 72% previously treated	15.6% at 7 years (18.6% if previously treated, 7.0% if ibrutinib was first-line). Not applicable to a newly diagnosed person

Sources: EHA 2026; VP8.2 §17.2; Ben-Dali 2020; Parikh 2013; Lenartova 2019; Pepe 2025.

[I] On the Danish figures, roughly 97 of 100 newly diagnosed people do not develop RT within 5 years. Mayo data hint that the risk may be lower in the targeted-therapy era, but the claim is not verified.

13.2 Risk factors¶

Established in at least two independent cohorts:

unmutated IGHV;
del(17p)/TP53 aberration;
advanced stage;
prior chemoimmunotherapy (combinations of purine analogues and alkylating agents raised the risk about three-fold).

Weaker or single-study evidence:

NOTCH1 mutation: a review quotes a 45% vs 4% cumulative risk, but the time horizon is unclear and the figure is not verified in the primary source.
Stereotyped subset #8: HR 24.5 (Rossi 2009).
Lymph nodes ≥3 cm: HR 6.5–9.1, from a single centre (Rossi 2008).
On ibrutinib: age under 70 (HR 1.98) and TP53 disruption (HR 1.72) (Pepe 2025).

13.3 Warning signs and diagnosis¶

Warning signs. Sweden's guideline and the 2025 ERIC consensus list the same signs [E] (VP8.2 §17.2; ERIC consensus 2025, abstract only):

rapid node growth at one or more sites;
pronounced B symptoms;
a marked LD rise;
rapid clinical decline.

A lower-tier review adds high blood calcium, a paraprotein, disease outside the lymph nodes (gut, marrow, central nervous system, skin), and anaemia or low platelets (Douglas 2022, Tier 3). In an Italian ibrutinib cohort, 60% had cytopenias when Richter was diagnosed (Pepe 2025). These signs overlap with ordinary progression, infections and second cancers. They are a reason to contact the team promptly, not proof of transformation.

Diagnosis requires tissue.

PET-CT helps choose the biopsy site. At an SUVmax threshold of about 5, pooled sensitivity was 0.90 and specificity 0.54; at about 10, 0.74 and 0.84 (Lee 2025). EHA calls the threshold "debated" for patients on targeted therapy.
Biopsy: excisional biopsy is preferred; a core-needle biopsy is used if excision is impossible. The work-up should include immunohistochemistry with EBV, flow cytometry, and a bone marrow sample.
Clonal relationship: this should be tested by comparing IGHV sequences. About 80% of DLBCL-type transformations are clonally related to the CLL.
TP53: aberrations are present in 50–60%.
Look-alikes to rule out: accelerated CLL (treated as CLL), and "pseudo-Richter", a temporary flare when a BTK inhibitor is paused.

13.4 Outlook and current treatment¶

Outlook depends heavily on the type of transformation and on prior treatment [E]:

Clonally related DLBCL-type RT: median survival 8–16 months (VP8.2). A Mayo series reported a median OS of 12 months: 46.3 months if the CLL had never been treated vs 7.8 months if it had (Wang 2020).
Danish national data, 2002–2022 (median OS after first-line treatment):
RT arising from untreated CLL: 5.22 years;
RT arising from previously treated CLL: 0.72 years;
de novo DLBCL, for comparison: 9.42 years (Katsimigas 2026).
Clonally unrelated RT: survived much longer in one series (62.5 vs 14.2 months) (Rossi 2011). A 2025 systematic review found this has not been shown to be independent of other factors (Barrett 2025).

Standard approach. A clinical trial comes first (EHA II, A; ERIC; VP8.2). Outside trials:

DLBCL-type: R-CHOP-type chemoimmunotherapy, with complete remissions in 5–38% and median OS rarely above a year.
Consolidation: allogeneic transplant for fit patients who respond.
Clonally unrelated DLBCL: treated like de novo DLBCL.
Hodgkin-type: treated by Hodgkin protocols.

Newer approaches, from single-arm or retrospective data only:

Approach	Result	Source
Zanubrutinib + tislelizumab (RT1)	Response 58.3%; 12-month OS 74.7%	RT1, Nat Med 2024
Atezolizumab + venetoclax-obinutuzumab (MOLTO)	Response 67.9%	MOLTO
Venetoclax + DA-R-EPOCH	Complete remission 50%; median OS 19.6 months	Davids 2022
Epcoritamab alone	Response 47.6%; 57.1% when used as first RT therapy	Kater 2026
Epcoritamab + R-CHOP	Response 73–77%	conference/press release
CD19 CAR-T (retrospective)	Complete remission ~46%; 2-year OS 38–47%	Kittai 2024
Pirtobrutinib	Response 50%	Wierda 2024

Richter trials near Skåne: CLL-RT1 recruits at Rigshospitalet; CLLRT2 (pirtobrutinib + epcoritamab vs R-CHOP) was authorised in Denmark on 18 March 2026 but had not started recruiting by 7 October 2026 (section 17).

13.5 Can it be prevented?¶

No. "There is no early intervention known to reduce the risk of Richter transformation" (Martino 2026). Starting CLL therapy early is not recommended for this or any other purpose. Whether targeted therapy lowers RT incidence compared with chemoimmunotherapy is unproven.

[I] The practical defence is knowing the warning signs and getting a prompt biopsy.