Nuno Sousa

High resolution melting analysis of KRAS, BRAF and PIK3CA in KRAS exon 2 wild-type metastatic colorectal cancer

BackgroundKRAS is an EGFR effector in the RAS/RAF/ERK cascade that is mutated in about 40% of metastatic colorectal cancer (mCRC). Activating mutations in codons 12 and 13 of the KRAS gene are the only established negative predictors of response to anti-EGFR therapy and patients whose tumors harbor such mutations are not candidates for therapy. However, 40 to 60% of wild-type cases do not respond to anti-EGFR therapy, suggesting the involvement of other genes that act downstream of EGFR in the RAS-RAF-MAPK and PI3K-AKT pathways or activating KRAS mutations at other locations of the gene.MethodsDNA was obtained from a consecutive series of 201 mCRC cases (FFPE tissue), wild-type for KRAS exon 2 (codons 12 and 13). Mutational analysis of KRAS (exons 3 and 4), BRAF (exons 11 and 15), and PIK3CA (exons 9 and 20) was performed by high resolution melting (HRM) and positive cases were then sequenced.ResultsOne mutation was present in 23.4% (47/201) of the cases and 3.0% additional cases (6/201) had two concomitant mutations. A total of 53 cases showed 59 mutations, with the following distribution: 44.1% (26/59) in KRAS (13 in exon 3 and 13 in exon 4), 18.6% (11/59) in BRAF (two in exon 11 and nine in exon 15) and 37.3% (22/59) in PIK3CA (16 in exon 9 and six in exon 20). In total, 26.4% (53/201) of the cases had at least one mutation and the remaining 73.6% (148/201) were wild-type for all regions studied. Five of the mutations we report, four in KRAS and one in BRAF, have not previously been described in CRC. BRAF and PIK3CA mutations were more frequent in the colon than in the sigmoid or rectum: 20.8% vs. 1.6% vs. 0.0% (P=0.000) for BRAF and 23.4% vs. 12.1% vs. 5.4% (P=0.011) for PIK3CA mutations.ConclusionsAbout one fourth of mCRC cases wild-type for KRAS codons 12 and 13 present other mutations either in KRAS, BRAF, or PIK3CA, many of which may explain the lack of response to anti-EGFR therapy observed in a significant proportion of these patients.

Patient-derived bladder cancer xenografts: a systematic review

Patient-derived tumor xenografts (PDTXs) are said to accurately reflect the heterogeneity of human tumors. In the case of human bladder cancer, few studies are available featuring these models. The best methodology to develop and the real value of the model remain unclear. This systematic review aims to elucidate the best methodology to establish and use PDTXs to study the characteristics and behavior of human bladder tumors. The value and potential application of these models are also addressed. A comprehensive literature search was performed to identify published studies using xenograft models directly established from human bladder cancer samples into mice. A total of 12 studies were included in the final analysis. All studies differed in design; the reported take rate varied between 11% and 80%, with the implantation via dorsal incision and with matrigel obtaining the higher take rate. Advanced stage and high-grade tumors were associated with increased take rate. Xenografts preserved the original tumor identity in the establishment phase and after serial passages. Although some studies suggest a correlation between engraftment success and clinical prognosis, evidence about the association between the response of xenografts to treatment and the clinical response of the tumor of origin is still missing. All methodological approaches resulted in the establishment of tumor xenografts with preservation of the original tumor identity but variable take rate. The time needed to establish the model and propagate xenografts to a number suitable for drug testing is the main limitation of the model, along with the success rate and lack of consistency in the early passages. Comparison between tumor response in mice and clinical outcome remains to be assessed.