Metastatic colorectal cancer from an epidemiological and immunological perspective

Abstract

Colorectal cancer (CRC) is the third most common type of cancer and around 8000 persons in Sweden get the diagnosis each year. One in five will have metastases at diagnosis, i.e., synchronous, and almost as many will develop metastases during follow up, i.e., metachronous. Median survival after diagnosis of metastatic CRC (mCRC) is 1-1.5 years. The most common metastatic locations are the liver, lungs, and peritoneum. When the extent of tumour spread in these organs is limited, surgical resection of the metastases may be feasible. Only a fraction of patients is treated with metastatic site surgery. The treatments are imperfect and puts the patient's body under major strain and risk. Despite this, prognosis of mCRC is largely dependent on if the primary tumour and metastases can be surgically removed or not.There is a need to increase our understanding of who benefits from the surgical treatments and who does not. Furthermore, previous research has shown that access to metastatic site surgery may be unequal. Lastly, a deeper understanding of the immune system's role in CRC could be crucial, as it influences disease progression and may be central to the discovery of novel treatment options. The overarching aim of this thesis is to improve the prognosis of patients with mCRC by deepening our understanding of the disease and its treatment through epidemiological and immunological approaches.Study I investigated overall survival of 131 patients with CRC and peritoneal metastases (PM) undergoing direct (without neoadjuvant chemotherapy) cytoreductive surgery and hyperthermic intraperitoneal chemotherapy with complete cytoreduction (CCO-1), between 2012 and 2019. The patients' PM were confirmed by histopathological examination, and potential extraperitoneal metastases treated before end of follow-up. The median overall survival was 40.3 months. In a multivariable model including potential prognostic factors, peritoneal carcinomatosis index > 16 was the only factor studied associated with decreased survival. The study showed that overall survival, from an institution with direct surgery as the standard, was similar to reported median overall survival from other recent cohorts where neoadjuvant chemotherapy was standard.Study II examined the association between hospital volume and metastatic site surgery for 9,968 adult patients diagnosed with synchronous mCRC in 2009- 2016, registered in the Swedish CRC database linkage CRCBaSe. Patients at high-volume hospitals were more often treated with metastatic site surgery. When adjusting for that high-volume hospitals were more often university hospitals, in addition to adjustment of identified confounders, only hospital level remained associated with chance of metastatic site surgery. In summary, being cared for at a hospital with proximity to metastatic site surgery, i.e., a university hospital increased the odds of receiving metastatic site surgery.In study III the association between sex and metastatic site surgery was investigated for 12,201 patients with synchronous mCRC diagnosed in 2007- 2016 and registered in CRCBaSe. Women received 23% less metastatic site surgery for mCRC despite adjusting for factors affecting patient selection, e.g., age, comorbidities, and primary tumour location. Furthermore, the effect of sex on receival of metastatic site surgery was modulated by hospital level and year of diagnosis. This indicates that non-biological reasons contribute to the sex- based differences observed in metastatic site surgery rates.In study IV the impact of patient income on cancer-specific survival after diagnosis of synchronous or metachronous mCRC was evaluated. In total, 33,498 patients diagnosed with CRC in 2007-2021 were identified using CRCBaSe, including follow-up throughout 2022. Patient income was associated with relative survival and the effect was time-varying with the largest impact in the first years after metastasis diagnosis. Furthermore, we found no support for a temporal trend affecting the impact of income on mCRC survival. Thus, patient income continues to be a factor associated with inferior survival after mCRC diagnosis.In study V we explored innate lymphoid cells (ILCs)' transcriptional patterns and differentiation capacities in tissue samples of primary colon cancer, PM from CRC, and macroscopically unaffected colon. Patients undergoing direct surgery for primary colon cancer and/or PM from CRC at Karolinska University Hospitals from 2020 were recruited. Single cell RNA sequencing of tissue samples from 11 patients revealed that primary colon cancer and CRC-PM are infiltrated by 14 transcriptionally different clusters of ILCs. In all three tissue types, two clusters of immature ILCs were present, annotated early NK cells and naïve ILCs. The naïve ILCs in tumours had more transcriptional similarities to ILCs type 1 (ILC1s) and tissue-resident natural killer cells, than ILCs from unaffected colon. We used a flow cytometry panel, based on the gene expression and surface protein signatures of the immature cells. Thereby, we could confirm the existence of the immature cell clusters in another patient population of eight patients contributing with seven primary tumours and seven colon tissue samples. The differentiation capacity of the immature cells was investigated using in vitro differentiation assays of an additional 14 patients contributing with paired primary tumour and unaffected colon samples. The experiments showed that naïve ILCs from primary colon tumours had an increased capacity to generate cells with a ILC1 or tissue-resident natural killer cell phenotype. Our findings contribute to the understanding of ILCs role in CRC and provides insights that could potentially be used in future therapies aiming to increase the innate immune response in CRC.List of scientific papersI. Direct surgery with Cytoreductive Surgery and Hyperthermic Intraperitoneal Chemotherapy for patients with Colorectal Peritoneal Metastases. Ljunggren M, Nordenvall C, Palmer G. Eur J Surg Oncol. 2021 Nov;47(11):2865-2872. https://doi.org/10.1016/j.ejso.2021.05.046II. Hospital factors and metastatic surgery in colorectal cancer patients, a population-based cohort study. Ljunggren M, Weibull CE, Rosander E, Palmer G, Glimelius B, Martling A, Nordenvall C. BMC Cancer. 2022 Aug 19;22(1):907. https://doi.org/10.1186/s12885-022-10005-8III. Sex differences in metastatic surgery following diagnosis of synchronous metastatic colorectal cancer. Ljunggren M, Weibull CE, Palmer G, Osterlund E, Glimelius B, Martling A, Nordenvall C. Int J Cancer. 2023 Feb 1;152(3):363-373. https://doi.org/10.1002/ijc.34255IV. Low income has a negative effect on survival following diagnosis of metastatic colorectal cancer – a population-based cohort study Ljunggren M, Dietrich CE, Merk C, Palmer G, Martling A, Nordenvall C. Cancer Med. [Accepted]V. Tumor-infiltrating immature innate lymphoid cells in colorectal cancer and peritoneal metastases are dysregulated and biased towards tissue-resident NK cell differentiation. Marchalot A, Ljunggren M, Weigel W, Stamper C, Tibbitt C, Meninger I, Vinay Pandey R, Franklin M, Ahlberg M, Lindforss U, Jansson-Palmer G, Nordenvall C, Mjösberg J. [Manuscript]</p