Molecular Detection of Bone Marrow (BM) Involvement in Primary Cutaneous B Cell Non Hodgkin’s Lymphoma (NHL) at Diagnosis.

Although the skin is the second most common site of involvement for extranodal lymphomas, only 20% of cutaneous NHL are of B cell origin. A wide range of B cell lymphomas can occur as primary cutaneous tumors and their clinical course can not always be predicted by histology alone. The incidence and significance of the presence of clonal B cell populations in the BM of affected patients at the time of diagnosis are presently unknown. On another hand, the BIOMED II primers were shown to have a high sensitivity for the detection of clonality in B cell lymphoproliferative disorders. We sought to determine the incidence of occult BM involvement in a series of twelve patients (3 women and 9 men, median age 54.5, 28 to 77 years old) diagnosed with primary cutaneous B cell lymphoma between August 2000 and May 2004, for whom skin biopsies, BM trephine biopsies and aspirates and clinical data were available for review. For that, we investigated the presence of clonal B cell populations in the BM aspirates obtained as part of the initial staging procedures by PCR (employing heteroduplex and GeneScanning analysis), using the BIOMED II primers for the immunoglobulin k light chain (IGK) and the immunoglobulin heavy chain complete and incomplete (IGH) rearrangements. At the same time, a set of amplified gene fragments of known sizes was run as a control of the DNA integrity. Patients’ diagnoses, according to the WHO classification, were marginal zone B cell lymphoma (5 cases), diffuse large B cell lymphoma (5 cases), follicular lymphoma (1 case) and NHL NOS (1 case). In all cases clinical evaluation, CT scans from the thorax, abdomen and pelvis as well as BM trephine biopsies failed to demonstrate extracutaneous involvement by NHL. Moreover, a maximum of 6% of policlonal CD19+ B cells were present in the BM aspirates as evaluated by flow cytometry. In three out of 12 cases (25%) a B cell clonal population was present in the BM, as demonstrated by the presence of an IGH clonal rearrangement detected by heteroduplex and/or GeneScanning analysis; they corresponded to two diffuse large B cell NHL cases and one marginal zone B cell lymphoma. Two of these patients are still under treatment and one (with diffuse large B cell lymphoma) remains in complete remission 9 months after first line therapy. In this small series of patients the detection of clonal B cell rearrangements in the BM analyzed at the time of diagnosis was uncommon; the clinical course of the positive cases did not differ from the whole series. Further follow-up studies are needed to define the significance and prognostic impact of those BM clones in cutaneous B cell NHL patients.