multiple myeloma (MM) is a malignant monoclonal plasma cell proliferation. Monoclonal gammopathy of unknown significance (MGUS) and smoldering myeloma (SMM) are premalignant states susceptible to transform in MM

phenotype of mature terminally differenciated B-cell, but also with CD56 expression, which is not found in normal plasma cells; CD138+.CD38+ CD40+

multiple myelomas annual incidence: 30/10⁶; i.e. around 1% of malignancies in adults and 10% of haematologic malignancies; mean age: 62 yrs

patients may be asymptomatic at the time of diagnosis; bone pain; susceptibility to infections; renal failure; neurologic dysfunctions

MM staging: stage I: tumour cell mass < 0.6 X 10¹²/m2; Hb> 10 g/dl; serum calcium ¾ 120 mg/l; no bone lesion; low monoclonal Ig rate (IgG < 50 g/l, IgA < 30 g/l, BJ urine < 4 g/day); stage II: fitting neither stage I nor stage II; stage III: tumour cell mass > 1.2 X 10¹²/m2; Hb< 8.5 g/dl and/or serum calcium > 120 mg/l and/or advanced lytic bone lesions and/or high monoclonal Ig rate (IgG > 70 g/l, IgA > 50 g/l, BJ urine > 12 g/day)

none before onset of symptoms; chemotherapy or BMT afterwards. Various new therapies, mainly acting by apoptosis induction in MM cells, are or will be involved in clinical trails (thalidomide, proteasome inhibitor PS-341, 2 methoxy estradiol, arsenic trioxyde, TNF alpha).

evolution: multiple myeloma can evolve towards plasma cell leukemia, where plasma cell count is greater than 2000/ mm3; survival is highly variable (median is around 3 yrs); prognosis is according to the staging and other parameters (such as age, serum albumin, b2 microglobulin, C-reactive protein, and plasma cell labeling index); the karyotype is emerging as an important prognostic factor: median survival in case of a normal karyotype could be 4 yrs vs 1 yr in case of -13/del(13q) and/or 11q rearrangements (the chromosome anomalies with the worst prognostic impact)

cytogenetic information is limited, as the malignant cells have a low spontaneous proliferative activity; abnormal karyotypes are found in 30-50% of cases, more often in advanced stages than in newly diagnosed patients (is this because chromosome abnormalities are secondary events, or because malignant cells have an increased proliferative activity in advanced stages: see below); karyotypes are complex; hyperploidy is found in 2/3 of cases; karyotypes may evolve from normal to abnormal during course of the disease;
- structural (and variable) anomalies of chromosome 1 are found in 30-40% of cases, 14q rearrangements in 25% of cases, 11q abnormalities in 20 %, t(11;14)(q13;q32) representing 10%; 6q anomalies represent 15% of cases; FISH is indicated, as metaphases are arduous to obtain in such a disease implicating mature cells, and tend to show that most cases bear chromosome anomalies, irrespective of the disease staging.

All MM cells should express chromosome abnormalities, as strongly suggested by interphase FISH and CGH.
Aneuploidy is detected in 67-90% of cases, allowing to define 2 prognosis entities:
1) hyperdiploid sub-group with a significantly better overall survival, gains involving primarily +3, +5, +7, +9, +11, +15, +19, +21 and infrequent structural abnormalities.
2) hypodiploid group (+hypotetraploid cases by endoreduplication of a prior hypodiploid karyotype) strongly correlated with complex structural rearrangements, 14q32 translocations, del(13q)/-13 and a more aggressive evolution.
IG rearrangements: translocations involving 14q32 are found in at least 65-70% of patients, most of them result from short segments exchange and are detected quite exclusively by FISH. Five translocations involving IGH locus are particularly relevant and considered as very early primary events: t(4;14)(p16;q32), t(6;14)(p25;q32), t(11;14)(q13;q32), t(14;16)(q32;q23), t(14;20)(q32;q11). Other translocations involving IGH are rare or sporadic, they should be secondary and not mediated by specific recombination mechanisms.
Del13q/-13: 13q14.3 deletions emerge as a major independant pronostic factor, underevaluated by conventional cytogenetics; found by FISH in 20-30% of patients; associated with a significant lower rate of response to conventional chemotherapy, and to a shorter survival.

see the more recent paper on Multiple Myeloma