Ben O'Leary

Treating cancer with selective CDK4/6 inhibitors

Uncontrolled cellular proliferation, mediated by dysregulation of the cell-cycle machinery and activation of cyclin-dependent kinases (CDKs) to promote cell-cycle progression, lies at the heart of cancer as a pathological process. Clinical implementation of first-generation, nonselective CDK inhibitors, designed to inhibit this proliferation, was originally hampered by the high risk of toxicity and lack of efficacy noted with these agents. The emergence of a new generation of selective CDK4/6 inhibitors, including ribociclib, abemaciclib and palbociclib, has enabled tumour types in which CDK4/6 has a pivotal role in the G1-to-S-phase cell-cycle transition to be targeted with improved effectiveness, and fewer adverse effects. Results of pivotal phase III trials investigating palbociclib in patients with advanced-stage oestrogen receptor (ER)-positive breast cancer have demonstrated a substantial improvement in progression-free survival, with a well-tolerated toxicity profile. Mechanisms of acquired resistance to CDK4/6 inhibitors are beginning to emerge that, although unwelcome, might enable rational post-CDK4/6 inhibitor therapeutic strategies to be identified. Extending the use of CDK4/6 inhibitors beyond ER-positive breast cancer is challenging, and will likely require biomarkers that are predictive of a response, and the use of combination therapies in order to optimize CDK4/6 targeting.

Early circulating tumor DNA dynamics and clonal selection with palbociclib and fulvestrant for breast cancer

CDK4/6 inhibition substantially improves progression-free survival (PFS) for women with advanced estrogen receptor-positive breast cancer, although there are no predictive biomarkers. Early changes in circulating tumor DNA (ctDNA) level may provide early response prediction, but the impact of tumor heterogeneity is unknown. Here we use plasma samples from patients in the randomized phase III PALOMA-3 study of CDK4/6 inhibitor palbociclib and fulvestrant for women with advanced breast cancer and show that relative change in PIK3CA ctDNA level after 15 days treatment strongly predicts PFS on palbociclib and fulvestrant (hazard ratio 3.94, log-rank p = 0.0013). ESR1 mutations selected by prior hormone therapy are shown to be frequently sub clonal, with ESR1 ctDNA dynamics offering limited prediction of clinical outcome. These results suggest that early ctDNA dynamics may provide a robust biomarker for CDK4/6 inhibitors, with early ctDNA dynamics demonstrating divergent response of tumor sub clones to treatment.Circulating tumor DNA (ctDNA) may provide a prediction of treatment response, but could be impacted by tumor heterogeneity. Here, the authors investigate ctDNA in CDK4/6 inhibitor treatment in advanced breast cancer, finding ctDNA levels predict progression-free survival and anticipate clonal selection.

Ultra-Sensitive Mutation Detection and Genome-Wide DNA Copy Number Reconstruction by Error-Corrected Circulating Tumor DNA Sequencing

BACKGROUND Circulating free DNA sequencing (cfDNA-Seq) can portray cancer genome landscapes, but highly sensitive and specific technologies are necessary to accurately detect mutations with often low variant frequencies. METHODS We developed a customizable hybrid-capture cfDNA-Seq technology using off-the-shelf molecular barcodes and a novel duplex DNA molecule identification tool for enhanced error correction. RESULTS Modeling based on cfDNA yields from 58 patients showed that this technology, requiring 25 ng of cfDNA, could be applied to >95% of patients with metastatic colorectal cancer (mCRC). cfDNA-Seq of a 32-gene, 163.3-kbp target region detected 100% of single-nucleotide variants, with 0.15% variant frequency in spike-in experiments. Molecular barcode error correction reduced false-positive mutation calls by 97.5%. In 28 consecutively analyzed patients with mCRC, 80 out of 91 mutations previously detected by tumor tissue sequencing were called in the cfDNA. Call rates were similar for point mutations and indels. cfDNA-Seq identified typical mCRC driver mutations in patients in whom biopsy sequencing had failed or did not include key mCRC driver genes. Mutations only called in cfDNA but undetectable in matched biopsies included a subclonal resistance driver mutation to anti-EGFR antibodies in KRAS, parallel evolution of multiple PIK3CA mutations in 2 cases, and TP53 mutations originating from clonal hematopoiesis. Furthermore, cfDNA-Seq off-target read analysis allowed simultaneous genome-wide copy number profile reconstruction in 20 of 28 cases. Copy number profiles were validated by low-coverage whole-genome sequencing. CONCLUSIONS This error-corrected, ultradeep cfDNA-Seq technology with a customizable target region and publicly available bioinformatics tools enables broad insights into cancer genomes and evolution. CLINICALTRIALSGOV IDENTIFIER NCT02112357.

Mismatch Repair as a Prognostic Marker for Adjuvant Therapy in Colorectal Cancer – How Soon is Now?

Treatment for colorectal cancer is guided principally by stage in a classification that has changed little over 70 years. Patients presenting with stage II and III resected colorectal cancer have no detectable metastatic disease, but a proportion of these patients will have undeclared micrometastatic disease, which it may be possible to eradicate with adjuvant treatment. Adjuvant chemotherapy with 5-fluorouracil (5-FU)based regimens was the standard of care for the treatment of stage III patients [1e3] and amodest benefit of oxaliplatin has been shown [4,5]. These studies also included high-risk stage II patients, but with a lower risk of relapse, even similar hazard ratios translate into small clinical benefit and the role for adjuvant chemotherapy remains debatable [6e8]. The largest study (QUASAR) suggested possible benefits of adjuvant chemotherapy of the order of 3e4% in overall survival for stage II patients [9], although of only marginal statistical significance. CALGB9581 (albeit investigating immunotherapy in this setting) confirmed the good prognosis of many patients with low-risk, stage II colorectal cancer [10]. Despite numerous emerging biomarkers, decisions on the potential benefits of adjuvant chemotherapy in stage II disease have used subjective analyses of adverse histopathological features (derived from the initial adjuvant 5-FU studies without subsequent validation). The hope is that biomarkers will allow better resolution of the heterogeneity thought to be present in colorectal cancer and, subsequently, more effectively targeted treatment. We believe there is now a strong case for routinely assessing mismatch repair (MMR) status in stage II colorectal cancer.

The Genetic Landscape and Clonal Evolution of Breast Cancer Resistance to Palbociclib plus Fulvestrant in the PALOMA-3 Trial

CDK4/6 inhibition with endocrine therapy is now a standard of care for advanced estrogen receptor-positive breast cancer. Mechanisms of CDK4/6 inhibitor resistance have been described preclinically, with limited evidence from clinical samples. We conducted paired baseline and end-of-treatment circulating tumor DNA sequencing from 195 patients in the PALOMA-3 randomized phase III trial of palbociclib plus fulvestrant versus placebo plus fulvestrant. We show that clonal evolution occurs frequently during treatment, reflecting substantial subclonal complexity in breast cancer that has progressed after prior endocrine therapy. RB1 mutations emerged only in the palbociclib plus fulvestrant arm and in a minority of patients (6/127, 4.7%, P = 0.041). New driver mutations emerged in PIK3CA (P = 0.00069) and ESR1 after treatment in both arms, in particular ESR1 Y537S (P = 0.0037). Evolution of driver gene mutations was uncommon in patients progressing early on palbociclib plus fulvestrant but common in patients progressing later on treatment. These findings inform future treatment strategies to address resistance to palbociclib plus fulvestrant.Significance: Acquired mutations from fulvestrant are a major driver of resistance to fulvestrant and palbociclib combination therapy. ESR1 Y537S mutation promotes resistance to fulvestrant. Clonal evolution results in frequent acquisition of driver mutations in patients progressing late on therapy, which suggests that early and late progression have distinct mechanisms of resistance. Cancer Discov; 8(11); 1390-403. ©2018 AACR. See related commentary by Schiff and Jeselsohn, p. 1352 This article is highlighted in the In This Issue feature, p. 1333.

Recalibrating emergency care in the UK: pulling our weight

Noticeably absent from the February Lancet Oncology Editorial were any suggestions for contributions that might be made by the oncology specialties to improve the situation in emergency care. A fi rm understanding of the problem is needed for a meaningful discussion of solutions. However, teasing apart the factors that contribute to the overwhelming of emergency services is diffi cult, and is more often dictated by confl icting political narratives than by the available evidence. The Editorial emphasises “better resourcing, co-ordination, and integration of GP services, secondary care, and social services”. In terms of co-ordination and integration of services, two ways exist for oncology services to ease pressure on emergency service, improve patient experience, and possibly improve even outcomes. The fi rst of these approaches is direct engagement of oncology specialists with emergency specialties through the establishment of acute oncology services. Data from one of the largest regional oncology networks in the UK showed that the introduction of an acute oncology service led to a reduction in the mean length of stay from 12·8 days to 9·7 days, an improvement of 24%. This extra capacity can be used to improve patient fl ow through the hospital to admit patients in accident and emergency more rapidly. These services are also well placed to identify common reasons cancer patients attend emergency services and to develop strategies to reduce attendances. The second approach is to improve engagement of oncology specialists with palliative care. In addition to the observed reduced emergency attendance in patients with palliative care support mentioned in the Editorial, early involvement with palliative care has been shown to improve quality of life, and even overall survival, in the setting of metastatic non-smallcell lung cancer. The additional fi nding by Temel and colleagues, whereby improved overall survival was associated with a signifi cant reduction in aggressive treat ment in terminal patients, makes uncomfortable reading for oncologists, especially with the increasing trend in aggressive end-of-life care and its associated increases in emergency department attendances. Oncologists are usually the gatekeepers of palliative care for patients with cancer, but often fail to communicate prognoses to patients or ensure realistic expectations for treatment, providing a barrier to the early involvement of palliative care. Early engagement with palliative care will benefi t both patients and oncology services alike. Doubtless key strategic decisions are needed to improve the situation in emergency care, but all health care specialties have a part to play, oncology included.

Converting Inoperable Colorectal Liver Metastases to Operable; Data from a UK Perspective.

Sir d Converting inoperable colorectal liver metastases (CLM) to become operable is an attractive option, as achieving surgical resection of liver metastases (� chemotherapy) can result in long-term remission and potentially cure [1,2]. Notably, however, the New EPOC trial [3] showed a reduction inprogression-free survival with the addition of cetuximab to chemotherapy. It remains unclear exactly how many patients are in a position to potentially benefit from conversion therapy. To address this we identified all new patients reviewed at a regional cancer centre multidisciplinary team in 2011, with a referral population of 500 000. Of 470 patients discussed, 414 had confirmed colorectal cancer and 34 had CLM. Of these, 29 were fit for systemic chemotherapy (16 were deemed operable pre-chemotherapy, 13 inoperable). Operable patients received CAPOX as first-line chemotherapy; three had a complete radiological response. Of the remaining 13 patients, three patients progressed, but then had a good response when changed to FOLFIRI þ biological agent. All 13 patients proceeded to liver resection. Of the 13 inoperable patients, six had a high burden of disease and were unlikely to be rendered operable by systemic therapy. The remaining seven were selected for conversion therapy (1.7% of the total population). Four of seven proceeded to liver resection, two converted with CAPOX, two converted with second-line chemotherapy, FOLFIRI and a biological agent (1� bevacizumab, 1� cetuximab). Therefore, only 1% of the colorectal cancer population comprised patients with initially inoperable CLM who later underwent hepatic resection with curative intent. These data suggest that the UK incidence of CLM suitable for conversion therapy is very low. Although a relatively small cohort, the resection rate in patients undergoing conversion therapy was similar to that seen in published series [4e6]. The successes in conversion therapy for CLM remain proof of principle, rather than a treatment strategy that can benefit many patients. The recent findings in New EPOC and the limited progress by adding other biological agents to chemotherapy suggest novel therapies will be required before conversion therapy becomes reality for a wider range of patients with colorectal cancer.

Another patient with low back pain.

A 52 year old man was admitted to our oncology unit owing to the side effects of ongoing chemotherapy; he also gave a 10 day history of back pain. In 2008, after a bowel resection for colonic obstruction, he had been diagnosed with diffuse large B cell lymphoma. This was treated with eight cycles of R-CHOP chemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone) and a complete response was achieved. He relapsed in 2010, when he presented with shortness of breath, lethargy, and weight loss. Imaging confirmed a pleural mass, lesions in the lung and liver, and lytic bone lesions. He received three cycles of RICE chemotherapy (rituximab, ifosfamide, carboplatin, and etoposide). After achieving a partial response he was treated with high dose cytarabine and etoposide chemotherapy to stabilise the disease. While he was an inpatient, with chemotherapy toxicity, he reported lower back pain and difficulty lifting his right leg, which had got worse over the past 10 days. The pain started suddenly when walking, woke him at night, and on walking radiated around to his umbilicus. On examination he was in pain—especially when he lifted the right leg—but had normal tone, power, reflexes, and sensation in both legs. A plain lumbar spine radiograph showed multiple lytic lesions, as expected. He therefore underwent magnetic resonance imaging of the whole spine (fig 1⇓). Fig 1 T2 weighted magnetic resonance imaging of lumbar spine