Transformation of Follicular Lymphoma to a High Grade B-Cell Lymphoma with MYC and BCL2 Translocations and Overlapping Features of Burkitt Lymphoma and Acute Lymphoblastic Leukemia

Most commonly, histologic transformation (HT) from follicular lymphoma (FL) manifests as a diffuse large B cell lymphoma, not otherwise specified (DLBCL, NOS). Less frequently, HT may result in a high-grade B cell lymphoma with MYC and BCL2 and/or BCL6 gene rearrangements, also known as "double-hit" or "triple-hit" lymphomas. In the 2016 revision of the WHO classification of lymphoid neoplasms, the category B-cell lymphoma, unclassifiable was eliminated due to its vague criteria and limiting diagnostic benefit. Instead, the WHO introduced the high-grade B-cell lymphoma (HGBL) category, characterized by MYC and BCL2 and/or BCL6 rearrangements. Cases that present as an intermediate phenotype of DLBCL and Burkitt lymphoma (BL) will fall within this HGBL category.

Very rarely, HT results in both the intermediate DLBCL and BL phenotype, and exhibits lymphoblastic features, in which case the WHO recommends that this morphological appearance should be noted. In comparison to de-novo patients with DLBCL, NOS, those with MYC and BCL2 and/or BCL6 gene rearrangements have a worse prognosis.

A 63-year-old female presented with left neck adenopathy. Lab assessment including complete blood count (CBC), complete metabolic panel (CMR), serum lactate dehydrogenase (LDH) and B-2 microglobulin were all normal. A whole body computerized tomography (CT) scan revealed diffuse adenopathy above and below the diaphragm. An excisional node biopsy showed grade 3A nodular FL. The Ki-67 labeling index was 40-50%. A bone marrow biopsy showed a small focus of para-trabecular CD20+ lymphoid aggregates.

She received 6 cycles of bendamustine (90 mg/m2 days +1 and + 2) and rituximab (375 mg/m2 on day+2) with each cycle delivered every 4 weeks. A follow up CT scan at completion of therapy showed a partial response with resolution of axillary adenopathy and a dramatic shrinkage of the large retroperitoneal nodes.

18 months later she had crampy abdominal pain in the absence of B symptoms. Positron emission tomography with 2-deoxy-2-[fluorine-18] fluoro- D-glucose integrated with CT (18F-FDG PET/CT) scan showed widespread adenopathy, diffuse splenic involvement and substantial marrow involvement. Biopsy of a 2.4 cm right axillary node (SUVmax of 16.1) showed involvement by grade 3A FL with a predominant nodular pattern of growth. A bone marrow biopsy once again showed only a small focus of FL.

She received idelalisib (150 mg twice daily), and rituximab (375 mg/m2, monthly) beginning May, 2015. After 4 cycles, a repeat CT scan showed a complete radiographic response. Idelalisib was subsequently held while she received corticosteroids for immune-mediated colitis. A month later she restarted idelalisib with a 50% dose reduction. Two weeks later she returned to clinic complaining of bilateral hip and low lumbar discomfort but no B symptoms. A restaging 18F-FDG PET/CT in January of 2016 showed dramatic marrow uptake. A bone marrow aspirate showed sheets of tumor cells representing a spectrum from intermediate sized cells with lymphoblastic features to very large atypical cells with multiple nucleoli. Two distinct histologies were present; one remained consistent with the patient's known FL with a predominant nodular pattern and the other consistent with HT (The large atypical cells expressed PAX5, CD10, BCL2, and cMYC, and were negative for CD20, MPO, CD34, CD30, and BCL6). Focal areas showed faint, heterogeneous expression of terminal deoxynucleotidyl transferase (TdT) best seen on the clot section. Ki67 proliferation index was high (4+/4). FISH analysis showed two populations with MYC amplification and/or rearrangement, and no evidence of BCL6 rearrangement; a karyotype analysis showed a complex abnormal female karyotype with t (14; 18) and multiple structural and numerical abnormalities.

She started dose-adjusted rituximab, etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (DA-R-EPOCH) with concomitant prophylactic intrathecal methotrexate and cytarabine. She had but a short lived response before dying in hospice from progressive lymphoma.

Whether idelalisib could provide a microenvironment for selection of more aggressive clones needs to be addressed. Our patient's clinical course is confounded by the incorporation of idelalisib while being further complicated by the complexity of HT and the mechanisms in which first-line chemotherapy regimens impact DHL.