Importance of Durable Response Rate for Cancer Treatment Trials

An objective response evaluation is a type of assessment that measures the response to a cancer treatment. This determines whether or not the agent or treatment method demonstrates a viable result that calls for further testing. This can measure clinical, as well as palliative effects, as patient comfort and symptom control can be taken into consideration. The main purpose to measuring objective response is to assure researchers that they are not overestimating response or success rates.

In regards to cancerous tumors, the method for assessment used is the Response Evaluation Criteria In Solid Tumors (RECIST). The guidelines for these means of clinical review were created through a collaborative project between the National Cancer Institute (NCI) of the US, the European Organisation for Research and Treatment of Cancer (EORTC) and the National Cancer Institute of Canada Clinical Trials Group. As a response to terminology set by the World Health Organization in the 1979, RECIST attempts to allow for better accuracy, in the evaluation of cancer trials. Here are some of the important terms related to RECIST and assessing the viability of prospective cancer treatments:

Partial Response Rate (PR): A partial decrease of at least 30% of the longest diameter of targeted cancerous lesions; sometimes also referring to a 30% decrease in the number of lesions. While this indicates that some disease remains in the patient, this demonstrates a marked change affected by treatment measures and allows researchers to gauge whether or not further development of the trial treatment method should be studied further.

Durable Response Rate (DRR): The length of time (usually displayed in months), that a partial or complete response is observed, as a result of treatment. Some melanoma treatment trials only show 2% of patients having a durable response, across all of the patients in a trial group, being that it is such a problematic disease to treat. A durable response is a good indicator that tentative treatment method has a lasting effect and may be a viable therapy, if coinciding with an improvement in overall survival.

Complete Response (CR): The complete resolution or disappearance of targeted cancerous lesions, through treatment. This means that no signs of cancer have been detected through any means of examination, body scans or testing. As this may not mean the cancer has been completely cured, it is sometimes referred to as “complete remission”.

Progression-free Survival (PFS): A “progressive disease” is considered one in which the longest diameter of a cancerous lesion has increased at by at least 20%, since treatment has started. Alternatively, “progression-free survival” measures the length of time after treatment has started where the cancer does not worsen or spread. This can be tied to durable response rate, as the patient is experiencing a marked decrease in the size of cancerous lesions over time, if the response to treatment is regarded as a at least a partial response.


OncoSec Merkel Cell Carcinoma Clinical Trial
We are still taking patients in our Phase II trial for Merkel cell carcinoma. See the trial page (click the picture), for more details.


The goal of most cancer trials is to reach a durable response rate, within the first two trial stages. Out of the treatment methods that are actually brought into practice, many trial treatments do not succeed. By performing due diligence through evaluations like RECIST, checks and balances are set up so that ineffective or dangerous treatments are not allowed to make it to the public. A durable response is critical in the fight against cancer, as the destruction or shrinkage of the majority of cancerous lesions shows a marked impact on patient health and well-being. The DRR is often used in publications to explain the outcome of cancer trials. It is important that the general public understands these terms, in order to best understand trial results.

OncoSec utilizes modified RECIST criteria for the evaluation of our clinical trials, as well as in press articles and releases to the general public. We are committed to developing treatment options that follow established medical guidelines, to ensure the safety of patients and maximize the success of treatment. In a release made today by OncoSec, interim data for our Phase II study of our ImmunoPulse system for metastatic melanoma treatment showed a 45% durable response rate, over 6 months, and a 68% durable response, over 3 months. This encouraging data shows an effective elimination of target tumors, along with a lasting effect.

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