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Background: Prostate cancer spinal bone metastases can have a radiographic profile that mimics multiple myeloma.

Objective: To analyse the presence and prognostic value of myeloma-like prostate cancer bone metastases and its relation to known clinical, molecular, and morphological prognostic markers.

Design, setting, and participants: A cohort of 110 patients with prostate cancer who underwent surgery for metastatic spinal cord compression (MSCC) was analysed. Spinal bone metastases were classified as myeloma like (n = 20) or non–myeloma like (n = 90) based on magnetic resonance imaging prior to surgery. An immunohistochemical analysis of metastasis samples was performed to assess tumour cell proliferation (percentage of Ki67-positive cells) and the expression levels of prostate-specific antigen (PSA) and androgen receptor (AR). The metastasis subtypes MetA, MetB, and MetC were determined from transcriptomic profiling.

Outcome measurements and statistical analysis: Survival curves were compared with the log-rank test. Univariate and multivariate Cox proportional hazard models were used to assess the effects of prognostic variables. Groups were compared using the Mann-Whitney U test for continuous variables and the chi-square test for categorical variables.

Results and limitations: Patients with the myeloma-like metastatic pattern had median survival after surgery for MSCC of 1.7 (range 0.1–33) mo, while the median survival period of those with the non–myeloma-like pattern was 13 (range 0–140) mo (p < 0.001). The myeloma-like appearance had an independent prognostic value for the risk of death after MSCC surgery (adjusted hazard ratio 2.4, p = 0.012). Postoperative neurological function was significantly reduced in the myeloma-like group. No association was found between the myeloma-like pattern and morphological markers of known relevance for this patient group: the transcriptomic subtypes MetA, MetB, and MetC; tumour cell proliferation; and AR and PSA expression.

Conclusions: A myeloma-like metastatic pattern identifies an important subtype of metastatic prostate cancer associated with poor survival and neurological outcomes after surgery for MSCC.

Patient summary: This study describes a novel radiographic pattern of prostate cancer bone metastases and its relation to poor patient prognosis.