Two BCL-2 Gene Variants Linked to Protein Levels and Aggressive Bladder Cancer

Bladder cancer remains one of the most common malignancies on the planet, ranking ninth in incidence worldwide and thirteenth in cancer-related mortality, yet clinicians still lack reliable molecular tools to predict which patients will see their tumors return after treatment. A new study from Brazilian researchers, published in Molecular Biology Reports, adds a promising piece to that puzzle by connecting two inherited variants in the BCL-2 gene — a master regulator of programmed cell death — to both protein expression in tumor tissue and the aggressiveness of urothelial bladder carcinoma, the most common histological form of the disease.

The research team, led by Julia Ayumi Ikeda Kawasaki of the State University of Londrina and Roberta Losi Guembarovski, focused on non-muscle-invasive bladder cancer, which accounts for roughly 75 percent of all cases. This category of the disease is notoriously frustrating to manage: recurrence rates range from 15 to 61 percent within the first year after resection and climb to 38 to 78 percent within five years. Despite these sobering figures, the field has struggled to identify robust prognostic biomarkers capable of flagging high-risk patients early, which is precisely why the researchers turned their attention to the genetics of apoptosis, the cellular self-destruct program that cancer cells must evade to survive.

BCL-2 sits at the heart of that evasion strategy. The protein it encodes is stationed on the outer mitochondrial membrane, where it binds to BAX, a pro-death protein, and thereby prevents the release of cytochrome C — the molecular trigger that would otherwise activate cytoplasmic caspases and dismantle the cell from within. When BCL-2 is overexpressed, malignant cells become effectively immortal, shrugging off the internal alarms that should spell their doom. The two variants examined in the study are single nucleotide polymorphisms, or SNPs: rs2279115, a G-to-T substitution located within the P2 promoter region of the gene, and rs3943258, a T-to-C substitution in an intronic segment previously shown to interact with histone marks such as H3K4me1 and H3K27ac, which influence chromatin accessibility and gene transcription.

To probe the functional significance of these variants, the team analyzed tissue samples and clinical data from 80 patients treated at the Londrina Cancer Hospital, dividing them into three groups: 19 with muscle-invasive tumors, 30 with non-muscle-invasive tumors that recurred, and 31 with non-muscle-invasive tumors that did not. Genomic DNA was extracted from buffy coat fractions of blood samples and genotyped using real-time PCR allelic discrimination assays on a StepOnePlus system, with TaqMan probes specific to each variant. Haplotype frequencies — the combinations of alleles inherited together on the same chromosome — were inferred with a Bayesian algorithm implemented in PHASE software, and only haplotypes exceeding 5 percent frequency were retained for statistical analysis to avoid the pitfalls of sparse data.

Protein expression was assessed through indirect immunohistochemistry on formalin-fixed, paraffin-embedded tissue blocks obtained by transurethral resection, with a board-certified pathologist scoring staining intensity as absent, weak, or strong in a blinded fashion. Palatine tonsil tissue and infiltrating lymphocytes served as positive controls, while selected samples were also examined by immunofluorescence to visualize weak and strong BCL-2 staining patterns directly. Across all malignant tissues, the protein localized exclusively to the cytoplasm of tumor cells, and most samples showed either absent or weak expression, prompting the researchers to pool weak and strong cases into a single positive-expression group for statistical power.

The genotyping results were striking. For rs2279115, the heterozygous GT genotype predominated at 53.8 percent of the cohort, while the wild-type GG genotype was least common at 21.3 percent. Statistical modeling revealed that this variant was significantly associated with positive BCL-2 expression: the TT genotype showed a significant link in the genotypic model (p = 0.035; OR 0.272) and the GT genotype in the overdominant model (p = 0.045; OR 0.398), suggesting that the presence of the T allele drives protein production. This finding fits neatly with the variant’s location in the P2 promoter region, where the T allele is thought to relieve transcriptional repression, and it echoes earlier reports that the TT genotype elevates BCL-2 levels in breast cancer patients. In contrast, the intronic rs3943258 variant showed no significant association with immunostaining in this cohort, leaving its functional role in bladder tissue an open question.

Perhaps the most consequential discovery emerged from haplotype analysis. Four haplotypes were inferred across the two SNPs — CG at 26.78 percent, TT at 28.22 percent, TG at 21.34 percent, and CT at 23.66 percent — and the CT combination turned out to be a significant risk factor for high-grade tumors. Patients carrying CT in either homozygous or heterozygous form faced roughly a threefold increase in the odds of harboring a high-grade malignancy (p = 0.020; OR 3.221; 95 percent CI 1.201 to 8.642), an effect that persisted after adjusting for biological sex, age, and smoking status. Because high histological grade signals a less favorable clinical outcome, this genetic signature could eventually help clinicians identify patients who warrant closer surveillance at the time of diagnosis. Notably, the researchers report that this specific haplotype-grade association has not been previously described.

Not every result pointed toward clinical utility, however. Kaplan-Meier survival analyses of recurrence-free survival — based on time-to-event data from 75 patients, including 37 recurrence events — showed no significant differences according to BCL-2 immunostaining intensity, TG haplotype status, or TT haplotype status. Cox proportional hazards models confirmed that neither staining intensity nor either haplotype profile was associated with the hazard of tumor recurrence, and exploratory interaction tests found no evidence that the effect of protein expression on survival depended on haplotype carrier status. The cohort itself was also largely unremarkable in its demographic risk profile: mean age was 69.55 years, 73.8 percent of patients were male, and 65 percent were non-smokers, but none of these variables showed a significant statistical association with muscle invasion or recurrence.

The authors are candid about the limitations of their work. The study was retrospective, long-term follow-up data were unavailable for survival analysis, and detailed treatment records — including tumor multiplicity, completeness of resection, intravesical therapy regimens, and surveillance intervals — were accessible for only a minority of patients, restricting the multivariable models. The sample size of 80 may also have underpowered the genetic analyses of individual polymorphisms against prognostic parameters, and nominal p-values were reported without formal correction for multiple comparisons, framing the findings as hypothesis-generating rather than definitive. Still, the team argues that the cohort size was well suited to the meticulous immunostaining work, and that the integrated approach — combining genotyping, haplotype reconstruction, and protein-level analysis — represents a methodological strength.

The bigger picture is one of cautious optimism. The study is, according to its authors, the first to investigate the interplay between BCL-2 allelic variants, haplotypic structures, and immunostaining profiles in urothelial bladder carcinoma, and it reinforces a growing consensus that combinations of SNPs — rather than single variants in isolation — may shape cancer biology in tissue-specific ways. Analogous BCL-2 haplotypes have been linked to leukemia susceptibility, lung cancer risk, and mortality outcomes, underscoring how context-dependent these genetic effects can be. If prospective studies in larger, fully annotated cohorts validate the CT haplotype as a marker of tumor aggressiveness and confirm the mechanistic link between the rs2279115 T allele and protein overexpression, BCL-2 profiling could one day serve as a complementary tool for risk stratification, helping urologists decide which patients need aggressive follow-up and which can be spared it. For now, the message is that the genetics of cell death may hold keys to predicting bladder cancer behavior — keys that are only beginning to turn.

Subject of Research: Association of BCL-2 gene polymorphisms and haplotypes with protein expression and clinical outcomes in urothelial bladder carcinoma

Article Title: Impact of BCL-2 rs2279115 and rs3943258 variants on protein expression and clinical outcome of urothelial bladder carcinoma

Article References: Kawasaki, J. A. I., de Souza, A. P., Pontes, J. P. R., Serpeloni, J. M., de Oliveira, J. N., Vanzela, A. L. L., Terziotti, F., Martinez-Lopez, W., de Oliveira, K. B., & Guembarovski, R. L. (2026). Impact of BCL-2 rs2279115 and rs3943258 variants on protein expression and clinical outcome of urothelial bladder carcinoma. Molecular Biology Reports, 53(1), Article 1544. https://doi.org/10.1007/s11033-026-12697-8

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12697-8

Keywords: BCL-2, urothelial bladder carcinoma, single nucleotide polymorphism, haplotype, apoptosis, immunohistochemistry, tumor recurrence, biomarkers, cancer genetics, promoter variant, tumor grade, prognosis