Tumor-Infiltrating Macrophages in Post-Transplant, Relapsed Classical Hodgkin Lymphoma Are Donor-Derived.

Tumor-associated inflammatory cells in classical Hodgkin lymphoma (CHL) typically outnumber the neoplastic Hodgkin/Reed-Sternberg (H/RS) cells. The composition of the inflammatory infiltrate, particularly the fraction of macrophages, has been associated with clinical behavior. Emerging work from animal models demonstrates that most tissue macrophages are maintained by a process of self-renewal under physiologic circumstances and certain inflammatory states, but the contribution from circulating monocytes may be increased in some disease states. This raises the question of the source of macrophages involved in human disease, particularly that of CHL. Patients with relapsed CHL following allogeneic bone marrow transplant (BMT) provide a unique opportunity to begin to address this issue. We identified 4 such patients in our archives. Through molecular chimerism and/or XY FISH studies, we demonstrated the DNA content in the post-BMT recurrent CHL was predominantly donor-derived, while the H/RS cells were derived from the patient. Where possible to evaluate, the cellular composition of the inflammatory infiltrate, including the percentage of macrophages, was similar to that of the original tumor. Our findings suggest that the H/RS cells themselves define the inflammatory environment. In addition, our results demonstrate that tumor-associated macrophages in CHL are predominantly derived from circulating monocytes rather than resident tissue macrophages. Given the association between tumor microenvironment and disease progression, a better understanding of macrophage recruitment to CHL may open new strategies for therapeutic intervention.

False positives in multiplex PCR-based next-generation sequencing have unique signatures.

Next-generation sequencing shows great promise by allowing rapid mutational analysis of multiple genes in human cancers. Recently, we implemented the multiplex PCR-based Ion AmpliSeq Cancer Hotspot Panel (>200 amplicons in 50 genes) to evaluate EGFR, KRAS, and BRAF in lung and colorectal adenocarcinomas. In 10% of samples, automated analysis identified a novel G873R substitution mutation in EGFR. By examining reads individually, we found this mutation in >5% of reads in 50 of 291 samples and also found similar events in 18 additional amplicons. These apparent mutations are present only in short reads and within 10 bases of either end of the read. We therefore hypothesized that these were from panel primers promiscuously binding to nearly complementary sequences of nontargeted amplicons. Sequences around the mutations matched primer binding sites in the panel in 18 of 19 cases, thus likely corresponding to panel primers. Furthermore, because most primers did not show this effect, we demonstrated that next-generation sequencing may be used to better design multiplex PCR primers through iterative elimination of offending primers to minimize mispriming. Our results indicate the need for careful sequence analysis to avoid false-positive mutations that can arise in multiplex PCR panels. The AmpliSeq Cancer panel is a valuable tool for clinical diagnostics, provided awareness of potential artifacts.

Clinical validation of KRAS, BRAF, and EGFR mutation detection using next-generation sequencing.

OBJECTIVES: To validate next-generation sequencing (NGS) technology for clinical diagnosis and to determine appropriate read depth. METHODS: We validated the KRAS, BRAF, and EGFR genes within the Ion AmpliSeq Cancer Hotspot Panel using the Ion Torrent Personal Genome Machine (Life Technologies, Carlsbad, CA). RESULTS: We developed a statistical model to determine the read depth needed for a given percent tumor cellularity and number of functional genomes. Bottlenecking can result from too few input genomes. By using 16 formalin-fixed, paraffin-embedded (FFPE) cancer-free specimens and 118 cancer specimens with known mutation status, we validated the six traditional analytic performance characteristics recommended by the Next-Generation Sequencing: Standardization of Clinical Testing Working Group. Baseline noise is consistent with spontaneous and FFPE-induced C:G→T:A deamination mutations. CONCLUSIONS: Redundant bioinformatic pipelines are essential, since a single analysis pipeline gave false-negative and false-positive results. NGS is sufficiently robust for the clinical detection of gene mutations, with attention to potential artifacts.

BRAF pyrosequencing analysis aided by a lookup table.

OBJECTIVES: BRAF mutations have substantial therapeutic, diagnostic, and prognostic significance, so detecting and specifying them is an important part of the workload of molecular pathology laboratories. Pyrosequencing assays are well suited for this analysis but can produce complex results. Therefore, we introduce a pyrosequencing lookup table based on Pyromaker that assists the user in generating hypotheses for solving complex pyrosequencing results. METHODS: The lookup table contains all known mutations in the sequenced region and the positions in the dispensation sequence at which changes would occur with those mutations. We demonstrate the lookup table using a homebrew dispensation sequence for BRAF codons 596 to 605 as well as a commercially available kit-based dispensation sequence for codons 599 to 600. RESULTS: These results demonstrate that the homebrew dispensation sequence unambiguously identifies all known BRAF mutations in this region, whereas the kit-based dispensation sequence has one unresolvable degeneracy that could be solved with the addition of two injections. CONCLUSIONS: Using the lookup table and confirmatory virtual pyrogram, we unambiguously solved clinical pyrograms of the complex mutations V600K (c.1798_1799delGTinsAA), V600R (c.1798_1799delGTinsAG), V600D (c.1799_1800delTGinsAT), V600E (c.1799_1800delTGinsAA), and V600_K601delinsE (c.1799_1801delTGA). In addition, we used the approach to hypothesize and confirm a new mutation in human melanoma, V600_K601delinsEI (c.1799_1802delTGAAinsAAAT).

Does BRAF V600E mutation predict aggressive features in papillary thyroid cancer? Results from four endocrine surgery centers.

BACKGROUND: Existing evidence is controversial regarding the association between BRAF mutation status and aggressive features of papillary thyroid cancer (PTC). Specifically, no study has incorporated multiple surgical practices performing routine central lymph node dissection (CLND) and thus has patients who are truly evaluable for the presence or absence of central lymph node metastases (CLNMs). METHODS: Consecutive patients who underwent total thyroidectomy and routine CLND at 4 tertiary endocrine surgery centers were retrospectively reviewed. Descriptive and bivariable analyses examined demographic, patient, and tumor-related factors. Multivariable analyses examined the odds of CLNM associated with positive BRAF status. RESULTS: In patients with classical variant PTC, bivariate analysis found no significant associations between BRAF mutation and aggressive clinicopathologic features; multivariate analysis demonstrated that BRAF status was not an independent predictor of CLNM. When all patients with PTC were analyzed, including those with aggressive or follicular subtypes, bivariate analysis showed BRAF mutation to be associated with LNM, advanced American Joint Committee on Cancer (AJCC) stage, and histologic subtype. Multivariable analyses showed BRAF, age, size, and extrathyroidal extension to be associated with CLNM. CONCLUSION: Although BRAF mutation was found to be an independent predictor of central LNM in the overall cohort of patients with PTC, this relationship lost significance when only classical variant PTC was included in the analysis. The usefulness of BRAF in predicting the presence of LNM remains questionable. Prospective studies are needed before BRAF mutation can be considered a reliable factor to guide the treatment of patients with PTC, specifically whether to perform prophylactic CLND.

Tandem duplication PCR: an ultrasensitive assay for the detection of internal tandem duplications of the FLT3 gene.

Internal tandem duplication (ITD) mutations of the FLT3 gene have been associated with a poor prognosis in acute myeloid leukemia. Detection of ITD-positive minor clones at the initial diagnosis and during the minimal residual disease stage may be essential. We previously designed a delta-PCR strategy to improve the sensitivity to 0.1% ITD-positive leukemia cells and showed that minor mutants with an allele burden of <1% can be clinically significant. In this study, we report on tandem duplication PCR (TD-PCR), a modified inverse PCR assay, and demonstrate a limit of detection of a few molecules of ITD mutants. The TD-PCR was initially designed to confirm ITD mutation of an amplicon, which was undetectable by capillary electrophoresis and was incidentally isolated by a molecular fraction collecting tool. Subsequently, TD-PCR detected ITD mutation in 2 of 77 patients previously reported as negative for ITD mutation by a standard PCR assay. TD-PCR can also potentially be applied to monitor minimal residual disease with high analytic sensitivity in a portion of ITD-positive acute myeloid leukemia patients. Further studies using TD-PCR to detect ITD mutants at diagnosis may clarify the clinical significance of those ITD mutants with extremely low allele burden.