The impact of cyclin D1 mRNA isoforms, morphology and p53 in mantle cell lymphoma: p53 alterations and blastoid morphology are strong predictors of a high proliferation index

Abstract

Background: Mantle cell lymphoma is a clinically heterogeneous disease characterized by overexpression of cyclin D1 protein. Blastoid morphology, high proliferation, and secondary genetic aberrations are markers of aggressive behavior. Expression profiling of mantle cell lymphoma revealed that predominance of the 3'UTR-deficient, short cyclin D1 mRNA isoform was associated with high cyclin D1 levels, a high "proliferation signature" and poor prognosis.

Design and methods: Sixty-two cases of mantle cell lymphoma were analyzed for cyclin D1 mRNA isoforms and total cyclin D1 levels by real-time reverse transcriptase polymerase chain reaction, and TP53 alterations were assessed by immunohistochemistry and molecular analysis. Results were correlated with proliferation index and clinical outcome.

Results: Predominance of the short cyclin D1 mRNA was found in 14 (23%) samples, including four with complete loss of the standard transcript. TP53 alterations were found in 15 (24%) cases. Predominance of 3'UTR-deficient mRNA was significantly associated with high cyclin D1 mRNA levels (P=0.009) and more commonly found in blastoid mantle cell lymphoma (5/11, P=0.060) and cases with a proliferation index of >20% (P=0.026). Both blastoid morphology (11/11, P<0.001) and TP53 alterations (15/15, P<0.001) were significantly correlated with a high proliferation index. A proliferation index of 10% was determined to be a significant threshold for survival in multivariate analysis (P=0.01).

Conclusions: TP53 alterations are strongly associated with a high proliferation index and aggressive behavior in mantle cell lymphoma. Predominance of the 3'UTR-deficient transcript correlates with higher cyclin D1 levels and may be a secondary contributing factor to high proliferation, but failed to reach prognostic significance in this study.

Figure 1.

Blastoid (A, C, E) and classic MCL (B, D). (A) Blastoid MCL shows large tumor cells with irregular large nuclei with open chromatin and a high mitotic rate (original magnification 400x) (C) MIB1 staining shows 80% positive tumor cells (case 3, original magnification 200x) (E) Virtually all tumor cells show strong expression of p53 protein (case 49, original magnification 200x) (B) Classical MCL shows cells with scant cytoplasm and small irregular nuclei (original magnification 400x) (D) MIB1 shows nuclear positivity in 13% of tumor cells (case 42, original magnification 200x).

Figure 2.

Scatter plots show the correlation between (A) proliferation index and blastoid morphology, (B) proliferation, morphological subtype and CyD1 isoform expression (red diamonds: predominant Δ3’UTR expression) and (C) proliferation, morphological subtype and p53 alteration (yellow diamonds: p53 overexpression/mutation).

Figure 3.

Relationship between p53 overexpression/mutation, Δ3’UTR cyclin D1 isoform expression, blastoid morphology and the proliferation index measured by MIB-1 immunostaining. Sixty-two MCL cases are ordered by MIB1 positivity (1–100% from left to right). Red squares in the upper three bars represent cases with p53 alteration, predominant Δ3’UTR cyclin D1 isoform expression and blastoid morphology, respectively.

Figure 4.

Overall survival analysis (Kaplan-Meier curves) of 51 MCL patients. (A) according to separation into three groups with high (>30% MIB1-positivity), medium (11–30% MIB1-positivity) and low proliferation index (0–10% MIB1-positivity), (B) separation into two groups with a cut-off of 10% as determined by maximally selected log-rank statistics (C) according to p53 status and (D) according to predominant cyclin D1 (CyD1) isoform expression.