Natural history of colorectal carcinoma: can the tumor volume doubling time be predicted by radiologic findings or immunohistochemical variables?

The pre-operative rate of growth of colorectal metastases in patients selected for liver resection does not influence post-operative disease-free survival

AIMS

To assess the potential association between the change in diameter of colorectal liver metastases between pre-operative imaging and liver resection and disease-free survival in patients who do not receive pre-operative liver-directed chemotherapy.

MATERIALS AND METHODS

Analysis of a prospectively maintained database of patients undergoing liver resection for colorectal liver metastases between 2005 and 2012 was undertaken. Change in tumour size was assessed by comparing the maximum tumour diameter at radiological diagnosis determined by imaging and the maximum tumour diameter measured at examination of the resected specimen in 157 patients.

RESULTS

The median interval from first scan to surgery was 99 days and the median increase in tumour diameter in this interval was 38%, equivalent to a tumour doubling time (DT) of 47 days. Tumour DT prior to liver resection was longer in patients with T1 primary tumours (119 days) than T2-4 tumours (44 days) and shorter in patients undergoing repeat surgery for intra-hepatic recurrence (33 days) than before primary resection (49 days). The median disease-free survival of the whole cohort was 1.57 years (0.2-7.3) and multivariate analysis revealed no association between tumour DT prior to surgery and disease-free survival.

CONCLUSIONS

The rate of growth of colorectal liver metastases prior to surgery should not be used as a prognostic factor when considering the role of resection.

Development and progression of colorectal cancer based on follow-up analysis

Elucidating the pathway of colorectal cancer development and progression can lead to identification of lesions that must be treated appropriately. The aim of the present review was to summarize the development and progression of colorectal cancer based on radiological and endoscopic follow-up analyses. These studies revealed several characteristic findings, including that initial morphology with progression to advanced cancer was most commonly 0-Is, followed by 0-IIa. Based on the doubling time, 0-Ip grew slowly in comparison with other morphologies. The observation period from adenomas measuring <10 mm to intramucosal cancers was more than 5 years. This makes it difficult to draw any accurate conclusions about the natural history of colorectal cancer based on follow-up observation alone and it is difficult to exclude the selection bias because of the difficulty of follow up for flat and depressed tumor. However, the only reliable way to elucidate the natural history is to accumulate cases.

A mathematical model of tumor-immune interactions

A mathematical model of the interactions between a growing tumor and the immune system is presented. The equations and parameters of the model are based on experimental and clinical results from published studies. The model includes the primary cell populations involved in effector T-cell mediated tumor killing: regulatory T cells, helper T cells, and dendritic cells. A key feature is the inclusion of multiple mechanisms of immunosuppression through the main cytokines and growth factors mediating the interactions between the cell populations. Decreased access of effector cells to the tumor interior with increasing tumor size is accounted for. The model is applied to tumors with different growth rates and antigenicities to gauge the relative importance of various immunosuppressive mechanisms. The most important factors leading to tumor escape are TGF-β-induced immunosuppression, conversion of helper T cells into regulatory T cells, and the limitation of immune cell access to the full tumor at large tumor sizes. The results suggest that for a given tumor growth rate, there is an optimal antigenicity maximizing the response of the immune system. Further increases in antigenicity result in increased immunosuppression, and therefore a decrease in tumor killing rate. This result may have implications for immunotherapies which modulate the effective antigenicity. Simulation of dendritic cell therapy with the model suggests that for some tumors, there is an optimal dose of transfused dendritic cells.

Long-term survivors of metastatic colorectal cancer treated with systemic chemotherapy alone: a North Central Cancer Treatment Group review of 3811 patients, N0144

BACKGROUND

Although systemic chemotherapy in patients with unresectable metastatic colorectal cancer (mCRC) is palliative in nature, some patients experience long-term remission beyond 5 years consequent to treatment with chemotherapy alone.

PATIENTS AND METHODS

We reviewed clinical data from 32 prospective North Central Cancer Treatment Group chemotherapy trials in mCRC that enrolled patients from 1972 to 1995. Metastatic CRC was verified histologically. Excluded from analyses were patients who withdrew consent to the study, enrolled in > 1 study, were ineligible, or had major protocol violations. We defined patients with survival beyond 5 years from the initiation of systemic treatment of mCRC as long-term survivors (LTS).

RESULTS

A total of 36 of 3407 (1.1%) patients were LTS. A total of 13 patients (0.4%) are without evidence of disease or disease progression > 5 years from cessation of last chemotherapy, with a median follow-up of 10.6 years (minimum, 7.6 years). Long-term survivors were more likely to have received 5-fluorouracil (5-FU)-based treatment (33 of 2503 [1.3%]) as opposed to other, less effective therapy (3 of 904 [0.3%]), suggesting that the chemotherapy played an important role among LTS (P = .01). Clinical characteristics of LTS were similar to the overall population in terms of age, sex, performance status, and tumor grade.

CONCLUSION

This study establishes a baseline for long-term outcomes of mCRC in the era when effective treatment was limited to 5-FU. With the development of improved systemic therapy for mCRC, cure without salvage surgery might be possible for a small, but important number of patients. Clinical trials should follow patients for > 5 years to document the long-term outcomes.