An Observational Study to Correlate the Results of Ploidy and Stroma Analysis With Prognosis in Early Rectal Cancer

Early rectal cancer can be removed by minimally-invasive surgery, and the standard pathological assessment of the removed tumour gives valuable information about how advanced the tumour is. This information is very important in indicating whether the cancer is likely to recur, and therefore in advising the patient after surgery whether further treatment is advisable, and if not, what is the most appropriate follow-up regime. However there is still a lot of uncertainty in these predictions about recurrence of the cancer, and better tests are being sought. This study aims to look at two further pathology tests, ploidy and stroma ratio in the tumour, and correlate these test results with outcome in patients who have had an early rectal cancer removed. This will allow the investigators to assess whether these two tests provide additional value in predicting outcome. If so, clinicians would be better able to advise patients with early rectal cancer about their prognosis and further management.

Routine histopathology analysis of a rectal cancer specimen removed at surgery includes assessment of tumour size, depth of invasion, vascular, lymphatic and perineural invasion, tumour involvement of resection margins and nodal involvement. This information is valuable in predicting outcome. For example, predicted rates of local recurrence at 36 months following local excision of rectal cancer by transanal endoscopic microsurgery (TEM) based on tumour size, depth of invasion and lymphatic invasion have been tabulated. However such models are not perfect, and leave room for improvement. Ploidy and stroma ratio are two further tests which have shown some promise in predicting outcome.

Ploidy refers to the number of sets of chromosomes in a cell nucleus. Most human cells are normally diploid, with two sets of 23 chromosomes. Abnormal tumour cells may have a different number of sets of chromosomes, or be aneuploid, having some replicated or deleted chromosomes. In general, aneuploidy in cancer cells is associated with a worse prognosis. An early study of DNA ploidy in rectal cancer using flow cytometry showed an independent but small predictive effective of aneuploidy on survival. Technological advances now allow more accurate and detailed assessment of ploidy. The DNA ploidy status of tumour cells in early ovarian cancer has been found to predict which patients will benefit from adjuvant chemotherapy after surgery to remove the ovarian tumour and is used routinely in some centres to aid in decision-making.

Stroma ratio refers to the tumour: stroma ratio. A lower proportion of tumour cells or, conversely, a higher percentage of stroma, in a cancer tends to be associated with a poorer prognosis. This ratio has been found to be strongly associated with tumour growth and invasion in colorectal cancers, and to independently predict survival in patients undergoing surgery to removal colorectal tumours. However previous studies have looked mainly at more advanced colon cancers, rather than early rectal cancers, and have used only cancer-related death as the endpoint, rather than looking at local recurrence and response to adjuvant treatments.