Incidence, Risk Factors, Treatment and Long Term Outcome of Refractory and First Relapse AML Patients in the OSHO Studies

Introduction:

Outcome of patients (pts) with refractory AML or following relapse is considered dismal and usually reported as refractory/relapsed. Here we analyzed long term outcome of refractory and relapsing pts separately over a 10 year (y) period from two prospective, non-age-limited, adult AML studies. Results have been published or presented previously as part of the German AML Intergroup studies^1,2. However, incidence, characteristics, treatment and outcome of refractory and relapsed pts have not been evaluated.

Patients and Methods:

A total of 1621 pts from the OSHO 2002 ≤60 y (n=740) and 2004 >60 y (n=881) with newly diagnosed AML (except acute promyelocytic leukemia) and eligible for chemotherapy were analyzed. The gender was male in 51.7% of pts. AML type was de novo in 66.6%, followed by secondary AML in 25.8% and therapy related in 7.6%. Cytogenetic risk status was normal in 47.9%, intermediate in 16.3%, unfavorable in 15.3%, monosomal in 12.6% and favorable in 7.9%. Molecular analysis revealed wildtype (wt) FLT3 in 80.9% and FLT3 ITD mutated (mut) in 19.1% of pts. NPM was mutated in 30.2% of 1124 pts.

In the AML 2002 and 2004 studies (NCT 01414231; NCT 01497002; NCT00266136), pts were randomly (9:1) assigned to remission induction by cytarabine (1 g/m² bid d 1, 3, 5, 7) and Idarubicin (AML 2002) 12 mg/m²/d d 1-3¹ or mitoxantrone (AML 2004) 10 mg/m²/d iv d 1 - 3² or to a common arm consisting of a 3+7 scheme ³. Pts in complete remission (CR) received consolidation and stem cell transplantation (HSCT) according to cytogenetic risk and donor availability^1,2. Pts with partial remission (PR) or non-response (NR) to two induction cycles were considered refractory. Pts achieving CR and relapsing thereafter were considered relapses and treated with MitoFlag or Flag-Ida⁴.

Results:

The majority of pts [median age 62 (range 17-87) y] entered CR or CRi after one or two induction cycles (n=1144; 70.6%). OS was 31.9 (29.5-34.4) % @5y and 26.0 (23.4-28.9) % @10y. Results were age dependent and superior in younger pts with an OS of 46.8 (43.1-50.7) % @5y compared to 19.3 (16.7-22.4) % @ 5y in elderly. Age, cytogenetics and NPM1 were determinants for CR and WBC (p<0,001), gender (p<0,05) and AML type (p<0,01) for OS. FLT3-ITD mut was an important determinant for relapse free survival in pts ≤60y.

A total of 238 (14.7%) of 1621 pts, 23.5% in the younger and 76.5% in the elderly study, were refractory (PR 60.1%, NR 39.9%). Pts had a median age of 66 (range 23-83)y. OS of refractory pts was 11.4 (7.9-16.6)% @5y, and dependent upon PR [(13.1 (8.1-21.1) % @10y] and NR [5.2 (2.1-12.6) % @5y; p=0.0003]. Intensive chemotherapy ± HSCT and hypomethylating agents (HMA) were able to induce CR in 24.8% of pts. CR and non-CR pts had an OS of 42.7 (31.4-58.2) % @5y and an OS of 3.7 (1.7-8.0) % @2y, respectively. Risk factors for OS in refractory pts were age and type of therapy (p<0.0001). Almost all long term survivors were treated with HSCT.

Of the 1144 CR/CRi pts, 582 relapsed 1-121 months (mts) after CR. Relapse occurred in 34.0% ≤6 mts, in 38,8% between 7-18 mts and in 12,2% >18 mts. Age, cytogenetic risk, type of AML, interval CR to relapse and HSCT were the dominant factors for relapse. CR2 was achieved after intensive chemotherapy ± HSCT, ± DLI and HMA in 227 pts (39.0%), 54.5% in the AML 2002 and 28.4% in the AML 2004. OS of relapsed pts was 13.8 (11.1 - 17.3) % @5y and 10.9 (7.4 - 16.2) % @10y and was higher in the younger with 23.4 (18.2-29.9) % @5y as compared to elderly pts 6.9 (4.4 - 11.0) % @5y. Pts with CR2 had a LFS of 24.9 (19.5-31.7) % @5y and was highest in patients <60y when intensive chemotherapy followed by HSCT was involved. Independent risk factors for OS in relapsed pts were age, cytogenetic risk, interval CR1 to relapse and type of therapy. Relapsed pts with HSCT in CR1 showed a trend for reduced survival.

Conclusions

Outcome of pts with refractory and relapsed AML is unsatisfactory but consistent >10% @5y. A differential response is observed in refractory and relapsed pts and is dependent upon PR, NR and the achievement of CR. Increase of CR rate in younger but especially in elderly pts with second generation TKI, reduction of TRM using FLT3-inhibitor monotherapy and the option to treat pts ineligible to chemotherapy promise better outcome in refractory and relapsed AML.

¹Büchner et al. JCO 2012; ²Niederwieser et al Blood 2016; ³Mayer et al. NEJM 1994; ⁴Thiel et al. Ann Oncology 2015