Persistent molecular remission of refractory acute myeloid leukemia with inv(16)(p13.1q22) in an elderly patient induced by cytarabine ocfosfate hydrate

The prognosis of relapsed acute myeloid leukemia (AML) in elderly patients is dismal, even if the AML exhibits a good prognostic karyotype, such as inv(16)(p13.1q22). We present a 72-year-old female with AML with inv(16)(p13.1q22) who suffered five episodes of relapse with temporary complete remission. Maintenance chemotherapy with oral cytarabine ocfosfate hydrate eventually produced persistent molecular complete remission of her AML that had not been induced by conventional regimens including intensive chemotherapy and low dose cytarabine therapy. The high level of tolerability to oral cytarabine ocfosfate hydrate may offer elderly patients with this type of AML a good chance for a cure. Electronic supplementary material The online version of this article (doi:10.1186/s13045-014-0100-6) contains supplementary material, which is available to authorized users.


Introduction
Acute myeloid leukemia (AML) with inv(16)(p13.1q22) is characterized by a favorable prognosis and good response to treatment with cytarabine [1]. The strategy of treatment for AML with inv(16)(p13.1q22) is based on a series of intensive chemotherapy, which is considered more curable than prolonged maintenance chemotherapy with low-dose anti-leukemic agents even in the elderly [2][3][4]. On the other hand, low-dose cytarabine therapy (LDAC) is recommended for elderly patients with AML who are not considered suitable for intensive chemotherapy [5][6][7][8], but LDAC can rarely induce persistent remission [9]. Once they relapse, their prognosis is usually dismal, even if the AML is associated with inv (16)(p13.1q22) [10,11].

Case presentation
In December 2006, a 72-year-old female was admitted to our hospital presenting with general malaise and dyspnea. A physical examination revealed anemic palpebral conjunctiva and purpura of the extremities. The complete blood count indicated severe anemia and thrombocytopenia as well as mild leukocytosis with 22.5% blast cells (Additional file 1). A bone marrow examination showed a total nucleated cell count of 41,000/μL with 67.0% blasts (Additional file 2: Figure S1A). A cytogenetic analysis of the bone marrow cells with G-banding showed 46,XX,inv(16)(p13.1q22) in all 20 dividing cells (Additional file 2: Figure S1B). Based on these findings, the patient was diagnosed as having AML with inv(16)(p13.1q22).
The patient achieved complete remission (CR) after one course of induction chemotherapy comprising behenoyl cytarabine and daunorubicin according to a study protocol [12] (Table 1). However, the AML relapsed four months after the completion of the last cycle of consolidation therapy. Re-induction chemotherapy using the same regimen as the first induction induced a second CR. Thereafter, the patient suffered four further episodes of relapse with temporary remission (Figure 1). The failure to achieve durable remission even with high-dose consolidation therapy and its toxicities prompted us to select palliative care with LDAC at the third relapse. After achieving the sixth CR, the patient declined further treatment with LDAC due to toxicity. Therefore, oral  cytarabine ocfosfate hydrate (SPAC) was started in order to maintain remission in November 2011. The SPAC therapy was not associated with any significant toxicity. The CBFB-MYH11 fusion mRNA in the peripheral blood became negative after twelve courses of SPAC therapy, which was terminated in October 2013. The patient has since remained in molecular remission without chemotherapy ( Figure 1).

Discussion
Our patient received lower doses of cytarabine and daunorubicin than the doses that are considered as standard doses for remission induction of AML with inv (16)(p13.1q22) nowadays, and the suboptimal doses of induction chemotherapy may be the cause of her early relapse. However, higher doses of cytarabine and daunorubicin may have put the 72-year-old woman's life in danger due to associated toxicities. The frail woman eventually went into deep remission after maintenance therapy with a cytarabine prodrug SPAC. SPAC has been shown to be as effective and tolerable as LDAC in treatment of AML [13][14][15], though its usefulness of SPAC is not well recognized because it is not available outside Japan. In this case, the AML cells were considered as highly sensitive to cytarabine because of repetitive achievement of CR induced by LDAC. Besides, SPAC was associated with fewer toxicities than LDAC (Table 1). LDAC requires the use of subcutaneous injections twice a day, but elderly patients often have difficulties visiting the hospital frequently. On the other hand, SPAC can be orally administered at home. These advantages enabled our patient to continue the maintenance therapy for two years and contributed to her persistent molecular remission. Thus, SPAC potentially offers a chance of cure for elderly patients with inv(16)(p13.1q22) without life threatening toxicities.

Consent
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.