Introduction

Multiple myeloma (MM) is a monoclonal plasma cell proliferative disorder and causes bone marrow infiltration or bone destruction, which is the most prominent feature of MM, occurring in approximately two-thirds of patients at diagnosis and in nearly all patients during their disease [1,2]. Quantifying the extent of bone marrow infiltration or bone destruction plays a key role in assessing tumor burden, guiding treatment, and evaluating prognosis [3]. Conventional radiography and computed tomography (CT) can visualize the number and size of bone destruction, but its sensitivity is limited because it cannot show bone marrow infiltration [4]. The limitation is now often complemented by fluorodeoxyglucose (FDG) positron emission tomography (PET)/ CT, which contains both tumor morphology and metabolism information. However, FDG PET/CT is expensive, radiative, insensitive to bone marrow infiltration and bone destruction located in the skull or ribs and has a high false-positive rate and false-negative rate [5-7]. Magnetic resonance imaging (MRI) is highly sensitive for detecting bone marrow infiltration because of the excellent soft-tissue contrast [8]. Moreover, whole-body (WB) MRI has been proved to have greater sensitivity and specificity in detecting bone marrow infiltration or bone destruction than FDG PET/CT [9]. There are five MRI patterns of bone marrow infiltration in MM: normal, focal, diffuse, combined focal and diffuse, and salt-and-pepper [10]. Previous studies have shown that the tumor burden and prognosis differ among five MRI patterns [11-14]. Subsequently, semi-quantitative tumor burden scoring methods based on MRI pattern began to emerge in MM. However, previous scoring methods had some controversies: (I) they did not cover all five MRI patterns (such as normal and salt-and-pepper patterns) [15], (II) the studies had variational scoring weight for the number and size of focal lesions [15,16], (III) scoring weight for diffuse and combined diffuse and focal patterns were not proper and did not correspond to their tumor burden [1,15]. WB MRI has the disadvantages of long scanning time, high requirements for technology and equipment, and difficult observation of humeral lesions due to limited field of view (FOV). MM lesions are mainly located in the axial skeleton, and the whole spine is the most affected area [17]. The whole spine scan is quick and convenient and is widely used in clinical practice as an alternative to the WB MRI. In our study, we try to develop a new, easy-to-implement scoring method for all five MRI patterns on whole spine scanning. We explored the prognostic significance of the new tumor burden score by evaluating its role in predicting the early treatment response and its association with the revised International Staging System (R-ISS) stage.

Methods

We prospectively recruited participants with newly diagnosed MM who were determined by the International Myeloma Working Group criteria (IMWG) from August 2020 to October 2022, collected their clinical data, and performed whole spinal MRI on them. We developed a new tumor burden scoring method according to the extent of bone marrow infiltration in five MRI patterns and calculated the tumor burden scores. Before treatment, all participants were divided into three groups based on the R-ISS stage, and then all participants were treated with one of the following first-line induction regimens: bortezomib, lenalidomide, dexamethasone (n = 43); bortezomib, dexamethasone (n = 9); bortezomib, thalidomide, dexamethasone (n = 6); bortezomib, cyclophosphamide, dexamethasone (n = 4). All participants were divided into good response [≥ very good partial response (VGPR)] and poor response (< VGPR) groups after four treatment cycles. Univariate (independent t test or Mann-Whitney U test and Chi-square test or Fisher’s exact test) and multivariate (logistic regression) analyses were used to identify independent predictors and then receiver operating characteristic (ROC) curve analyses were performed. The Kruskal-Wallis H test was used to compare the differences of tumor burden score between R-ISS stages.

Results

The new tumor burden scoring method was used in 62 participants to assess their tumor burden (median score, 12; range, 0-18). The β2-microglobulin, creatinine, tumor burden score and R-ISS stage were significant different between two treatment response groups (all p < 0.05). The tumor burden score (odds ratio 1.276, p = 0.001) was an independent predictor of poor response and the area under the curve (AUC) was 0.842. The tumor burden score was higher in R-ISS-III stage than in R-ISS-I and R-ISS-II stages (p = 0.016, p = 0.006 respectively).

Conclusions

We developed a new tumor burden scoring method applicable to five patterns of bone marrow infiltration and calculated the tumor burden score. The tumor burden score was an excellent predictor of early treatment response and may serve as a supplemental marker for the R-ISS.

Acknowledgements

No acknowledgement found.

References

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