Mucin-1 (MUC-1) is a transmembrane glycoprotein that is normally present on the luminal surface of secretory glands (Patton et al, 1995), and a soluble form (sMUC, CA15·3) is found in breast milk, peripheral blood, urine, supernatants from cultured MUC-1 cancer cell lines, and primary cancer cells (Patton et al, 1995). High serum sMUC-1 levels have been detected in adenocarcinoma patients and seem to correlate with tumour burden (Hayes et al, 1985; Colomer et al, 1989; Price et al, 1990; Vizcarra et al, 1996). It has also recently been shown that patients with multiple myeloma (MM) have high peripheral blood and bone marrow levels of MUC-1, and that the latter directly correlate with tumour mass (Treon et al, 1999). To define the prevalence of high sMUC-1 levels in patients with plasma cell dyscrasias, we tested patients with MM, plasma cell leukaemia (PCL) or monoclonal gammopathy of undetermined significance (MGUS). We also evaluated the possible prognostic role of sMUC-1 levels in such patients.
Summary. High serum Mucin-1 (sMUC-1) levels have been shown in patients with adenocarcinoma and multiple myeloma (MM). We evaluated sMUC-1 levels in 76 patients with MM, 6 with plasma cells leukaemia (PCL) and 89 with monoclonal gammopathy of undetermined significance, to establish prevalence data and verify its possible prognostic role. Of the 171 patients, 27 [16%; 95% confidence interval (CI): 10–21%] had high sMUC-1 levels compared with healthy subjects (1·5%; 95% CI: 0–4%). Elevated sMUC-1 levels in MM and PCL patients correlated with anaemia and elevated serum lactate dehydrogenase levels; these patients showed a shorter survival than those with normal sMUC-1 levels (median overall survival: 25 vs. 49 months, P = 0·003).
Patients and methods
Peripheral blood serum samples were collected at the time of first contact or at any time during follow-up from 89 consecutive MGUS patients referred to us between 1999 and 2001: 45 immunoglobulin (Ig)G, 23 IgA and 19 IgM with a mean serum monoclonal component (MC) concentration 13·7 g/l, 9·5 g/l and 10 g/l respectively; κ/λratio: 2·12; male/female ratio: 0·44; median age 64 years, range 27–90 years. Their clinical data were also recorded at the same time. We also analysed stored serum aliquots, collected at diagnosis, from 76 MM and 6 PCL patients consecutively admitted to our Institution between 1991 and 2002 (Table I); samples obtained from 65 age- and sex-matched, healthy subjects attending our Transfusion Department were also evaluated. All samples were tested with an automated competitive chemoluminescent assay using B27·29 antibody against MUC-1 protein (Immunolite; DPC, Los Angeles, CA, USA). To verify the possible role of the different patterns of MUC-1 glycosylation in myeloma plasma cells (Treon et al, 1999), the sera from the MM/PCL patients were also tested using an Abbot IMX CA15·3, a Boehringer Mannheim Enzymmun CA15-3 and a Centrocor CA15-3, according to the manufacturers' protocols. The statistical analyses were made using the Statistical Package for Social Sciences (SPSS) Version 10·0. Proportions were compared using Fisher's exact test. The four sMUC-1 assay methods were compared using one-way analysis of variance (anova) and Bonferroni's test. Survival was analysed using the Kaplan–Meyer method and the survival rates compared by means of the log-rank test. The statistical significance of the measured differences was determined using an alpha index of 0·05.
|All patients||Patients with normal sMUC-1 levels||Patients with elevated sMUC-1 levels||P-value|
|Number of patients||82||66||16|
|Median age, years (range)||67 (26–80)||67 (45–80)||63 (26–74)||0·17|
|Age > 60 years (n)||43||35||8||0·5|
|Number of males||41||30 (46)||11 (69)||0·08|
|BJ proteinuria||18||11 (17)||7 (44)||0·13|
|↓ polyclonal serum Ig||61||47 (71)||14 (87)||0·06|
|I||24||17 (26)||7 (44)|
|II||24||21 (32)||3 (19)|
|III||34||28 (42)||6 (37)||0·5|
|A||74||60 (91)||14 (88)|
|B||8||6 (9)||2 (12)||0·5|
|High β2-M levels||61||48 (73)||13 (81)||0·32|
|Hb < 11 g/dl||44||31 (47)||13 (81)||0·01|
|High LDH levels||8||3 (4)||5 (31)||0·006|
Results and discussion
Carcinoma sMUC-1 levels are biologically important because their possible immunomodulatory role may contribute to tumour progression (MacLean et al, 1997). In breast cancer patients, sMUC-1 levels correlate with tumour mass, and CA15·3 assays have been approved by the Federal Drugs Administration, USA, for monitoring disease. Treon et al (2000) have shown a correlation between sMUC-1 levels, tumour burden and disease activity in patients with plasma cell malignancies, but there are no data concerning sMUC-1 levels in preneoplastic conditions such as MGUS or their prognostic relevance in terms of survival. In comparison with the normal ranges of the Immulite test (< 51 U/ml), high sMUC-1 levels were found in 11/89 subjects with MGUS [12·4%; 95% confidence interval (CI): 5·5–19·2], 13/76 with MM (17·1%; 95% CI: 8·6–25·6) and 3/6 with PCL. In the healthy control group, only one subject had high levels (1·5%; 95% CI: 0–4%); this difference was statistically significant (P = 0·001). The mean sMUC-1 levels were significantly higher in the MC-carrying patients than in the healthy subjects (43·2 vs. 26 U/ml; P = 0·001). There was a trend towards a greater prevalence of high sMUC-1 levels in the patients with IgM class protein (4/20) and those with light chain MM (3/7) than in those with IgG (15/101) or IgA (5/39); the prevalence was similar between those with kappa (21/115) and lambda light chain monoclonal protein (6/53). The median follow-up of the 82 MM/PCL cases was 30 months (range 6–114), during which 51 patients died: 39/66 (59%) with normal and 12/16 (75%) with high sMUC-1 levels. The median overall survival (OS) was 44 months. There was a difference in OS between the MM/PCL patients with normal or increased sMUC-1 levels: median OS 49 vs. 25 months, 3-year OS 63% and 25% (P = 0·036) (Fig 1).
Increased sMUC-1 levels correlated with some features that are associated with high tumour burden, such as anaemia and high serum lactate dehydrogenase levels (Table I), but a larger series is necessary to test whether these factors represent independent prognostic factors at multivariate analysis. Given the short follow-up of the MGUS patients (median 12 months; range 6–30) and the absence of any MM transformation during this time, no conclusions can be drawn concerning a possible correlation between high sMUC levels and the relative risk of MM evolution. Further analyses are required, but our results suggest that MUC-1 could have a role in tumour progression; the fact that high levels are very frequently associated with a diagnosis of PCL indicates a possible relationship between them and tumour malignancy (cell proliferation, genetic instability), and this could also explain the association of increased sMUC levels with the subgroup of MM patients with a worse prognosis and higher tumour burden. Some authors have recently demonstrated an inverse correlation between sMUC-1 levels and IgM anti-sMUC-1 in ovarian cancers and plasma cells neoplasms (Richards et al, 1998; Treon et al, 2000), suggesting that MUC1 may have a role as an immunosuppressant agent in tumour progression.
Finally, many authors have reported a different MUC-1 protein glycosylation pattern in myeloma plasma cells from that of the protein expressed by epithelial cells, thus suggesting that sMUC-1 determinations may be affected by the assay method: the various antibodies used in sMUC-1 assays recognize distinct antigen epitopes and their different degrees of reactivity may depend on the extent of the glycosylation of the CA15·3 antigen. In our MM patients evaluated using different methods, we found differences in absolute values, but multiple comparisons (Bonferroni's test) showed a high degree of correlation (data not shown).
In conclusion, this study shows that a subset of MM and MGUS patients, and most PCL cases, had increased sMUC-1 levels. In patients with overt plasma cell neoplasia, high sMUC-1 levels identified a group with a poor prognosis.
We thank Nadia Zucal for freezing the patient's sera.