Encrypted Cancer Genomics: Benchmark Reveals Speed Versus Storage Tradeoff in Homomorphic Encryption

Genomic medicine has a privacy problem that is getting harder to ignore. As hospitals and research consortia increasingly hand RNA-sequencing data to cloud platforms for large-scale analysis, the sensitive molecular profiles of cancer patients travel beyond institutional walls, where they become attractive targets for re-identification and misuse. A new study published in BMC Bioinformatics offers a rigorous empirical answer to one of the most promising technical fixes: fully homomorphic encryption, or FHE, a cryptographic technique that allows computation directly on encrypted data without ever decrypting it. The work, conducted by Dilen Shankar of the Department of Computer Technology at Anna University in Chennai, India, provides the kind of systematic, head-to-head benchmarking that the field has lacked, and its findings reveal a striking tradeoff between speed and storage that will shape how privacy-preserving genomics pipelines are built.

The appeal of fully homomorphic encryption in genomics is straightforward to state but difficult to achieve in practice. Differential expression analysis, one of the most common first steps in cancer transcriptomics, compares gene expression levels between groups of samples, such as tumor tissue versus healthy tissue, to identify genes whose activity changes with disease. Because expression profiles are inherently identifying, uploading raw count matrices to a third-party cloud service exposes patients to real risk. FHE promises to dissolve that risk: the cloud server performs the statistical computation on ciphertexts, and only the data owner, holding the secret key, can decrypt the results. The catch is cost. Homomorphic operations are orders of magnitude slower than their plaintext equivalents, and the exact penalty depends heavily on which encryption scheme is chosen and how its parameters are configured.

The study focuses on the two most widely deployed FHE schemes, BFV and CKKS, which take philosophically different approaches to arithmetic on encrypted data. BFV operates on exact integers, making it well suited to the raw integer counts that RNA-seq pipelines produce, but it requires careful quantization when computations produce fractional values. CKKS, by contrast, works natively with approximate real numbers, embedding a scaling factor into each plaintext and accepting a small, controlled amount of noise with every operation. That approximation is usually negligible for statistical work, but it accumulates through a process called rescaling, and the new research shows that this accumulation can become measurable under certain parameter settings. Until now, the field has had little empirical guidance on when each scheme’s weaknesses matter more than its strengths.

To settle the question, the author designed a benchmark of unusual thoroughness for the FHE-genomics intersection. Two cancer RNA-seq datasets served as testbeds: the UCI Gene Expression RNA-Seq dataset, comprising 801 samples spanning five cancer types and yielding ten pairwise class comparisons, and the TCGA lung cancer dataset combining lung squamous cell carcinoma and lung adenocarcinoma, with 1,129 samples and a single pairwise comparison. Experiments swept across polynomial modulus degrees of 4,096, 8,192 and 16,384, the parameter that largely determines both security headroom and computational cost, and across three cohort sizes. Every configuration was run ten independent times under parameters compliant with the 128-bit security standard, the widely accepted benchmark for practical cryptographic deployments, for a total of 300 runs. That repetition matters, because FHE timings can be noisy and single-run benchmarks have historically overstated the reliability of performance claims.

The headline result is a decisive speed advantage for BFV. Across every configuration tested, BFV completed the full encrypt-compute-decrypt cycle in 3.5 to 7.5 times less total latency than CKKS. For teams weighing the practicality of encrypted differential expression analysis, that gap is not a rounding error; it can be the difference between a pipeline that finishes overnight and one that stalls for days. Yet the story does not end there. CKKS fought back on a different axis: at the largest polynomial modulus degree of 16,384, its ciphertexts were approximately 2.66 times smaller per sample than BFV’s. In cloud environments where storage and bandwidth are billed by the gigabyte, and where genomic cohorts can involve tens of thousands of samples, that storage advantage translates directly into cost savings and faster data transfer. The study’s central conclusion is that neither scheme is universally dominant; the right choice depends on whether a deployment is latency-bound or storage-bound.

Perhaps the most surprising finding concerns what actually drives computational cost. Intuition suggests that processing more samples should take proportionally longer, but the benchmark showed that execution time scaled primarily with the number of pairwise class comparisons rather than with sample count. In the UCI dataset, with its ten pairwise comparisons, the encrypted computation was far heavier than in the TCGA comparison, despite the latter containing more samples. This is a genuinely counterintuitive result that had received little attention in prior FHE benchmarking studies, and it carries immediate practical implications: analysts designing privacy-preserving pipelines for multi-class cancer studies should budget their computation around the number of group contrasts, not the size of the cohort, and should consider consolidating comparisons wherever the science allows.

Accuracy, the other half of the tradeoff equation, behaved in scheme-specific ways that the author traced to the underlying mathematics. CKKS’s approximation error grew worse at higher polynomial modulus degrees, a consequence of scale-induced rescaling noise accumulating through the computation. BFV, working with exact integers, showed the opposite and rather elegant behavior: its quantization noise decreased as cohort size increased, because averaging over more samples smooths out the rounding error introduced when fractional statistics are mapped onto the integer plaintext space. These opposing error dynamics mean that the accuracy picture changes with both the scheme and the scale of the study, and pipeline designers cannot simply assume that bigger parameters yield better results.

Crucially, however, the study delivers a reassuring bottom line for biomedical validity. Across all 300 runs and every configuration tested, both BFV and CKKS preserved the ranking of differentially expressed genes with a Spearman rank correlation above 0.999 relative to the plaintext baseline. In other words, even where numerical errors crept in, the biological conclusions, which genes rise to the top of the differential expression list, remained essentially identical to what an unencrypted analysis would produce. For clinical and research applications, that ranking fidelity is arguably the metric that matters most, and the result suggests that FHE-based privacy protection need not come at the price of scientific correctness.

Beyond the specific numbers, the study establishes a reproducible benchmarking framework that other researchers can extend to additional schemes, datasets, and statistical tasks. The author acknowledges Dr. Sudhakar Theerthagiri of Anna University’s MIT Campus for guidance on cryptography and methodological decisions, and the work received no external funding. Published open access on 15 September 2026, the paper arrives at a moment when privacy regulation and cloud genomics are colliding with growing force. As sequencing costs continue to fall and multi-institutional cancer studies become the norm, the demand for computation on encrypted genomes will only intensify. This benchmark gives the field its clearest map yet of the terrain: BFV for speed, CKKS for storage, class comparisons as the true computational driver, and gene rankings that survive encryption essentially intact. For a discipline wrestling with how to share its most sensitive data without giving it away, that map is a valuable piece of infrastructure in its own right.

Subject of Research: Privacy-preserving differential expression analysis of cancer RNA-seq data using fully homomorphic encryption

Article Title: Privacy-preserving differential expression analysis via fully homomorphic encryption: a systematic tradeoff evaluation of BFV and CKKS on cancer RNA-seq datasets

Article References: Shankar, D. (2026). Privacy-preserving differential expression analysis via fully homomorphic encryption: a systematic tradeoff evaluation of BFV and CKKS on cancer RNA-seq datasets. BMC Bioinformatics. https://doi.org/10.1186/s12859-026-06609-7

Image Credits: AI Generated

DOI: 10.1186/s12859-026-06609-7

Keywords: fully homomorphic encryption, BFV, CKKS, differential expression analysis, RNA-seq, cancer genomics, data privacy, transcriptomics, cloud computing, TCGA, genomic pipelines, cryptography