GTx, Inc. (NASDAQ:GTXI) just reported that it had me a stage 1 milestone in the investigation of its lead ER+/AR+ Breast Cancer asset, and the company is      up a few points on the news. The real data, however, is set to be reported next month, and that’s where the upside lies for the company and its shareholders.

With this in mind, and ahead of the data hitting press, let’s take a look at the drug, and see what the primary consideration are come release time.

Here goes.

As mentioned, the drug is an investigational breast cancer drug, and it’s called enobosarm, or GTx-024. The drug is part of a family of oncology therapies currently under investigation across a host of various cancer types in biotech, called androgen receptor modulators, or selective androgen receptor modulators (SARM) when applies to things like breast cancer and prostate cancer. Estrogen is linked to breast cancer spread, and the control of estrogen supply to tumor cells is pretty much the cornerstone of any type of cancer treatment outside SOC. SARMs such as enobosarm bind to what are called androgen receptors, and then can interact with a receptor-specific segment of DNA that controls gene expression. Through this interaction, the drug is able to compete with the binding of estrogen receptor to hormonally responsive DNA sites, and inhibit the transcription of ER-responsive genes. Inhibit this process, and the theory is that you can slow, or even halt, the progression of breast cancer of this type.

The drug has proved some degree of clinical benefit I what amounted to a phase II proof of concept study, although the degree to which it can impact patient survival still remains uncertain. Basically, out of 22 evaluable patients in the proof of concept trial, 17 proved AR+ (this treatment, as mentioned above, is targeting AR+ patients) meaning the evaluable patient population effectively reduced to 17. Of these 17, six demonstrated clinical benefit at six months. There was an extra patient that demonstrated clinical benefit, but that patient’s AR status wasn’t confirmed, making it tough to include this one in the data with any clarity.

So, 7 out of 17 derived meaningful benefit.

That’s not great, but it’s not terrible either, especially when it comes to an indication like this. The purpose of the study for which the news hit hit press is to build on this data, and try to bolster the impact numbers. It’s looking at a potential total of 88 evaluables, and it’s split into two stages, stage 1 and stage 2.

Stage 1 is based on 18 patients, treated daily with an oral dose for up to 24 months. Here’s the important part – if at least 3 of these patients showed clinical benefit, the company would move on to stage 2 and continue the trial (two cohorts, one low one high dose) until 88 patients had been evaluated.

The news just released outlined the fact that the company had hit clinical benefit in three patients, meeting its predefined threshold for stage 1, and is therefore able to kick off stage 2.

For reference, and this is also important, clinical benefit is defined as a complete response, partial response, or stable disease, as measured by Response Evaluation Criteria in Solid Tumors (RECIST) at 24 weeks. So this plays into what we are looking for come December, which is (as mentioned above) when the company is hoping to put out topline from the stage 1 part of the phase II study. Basically, we will see what degree of response the 3 (or more) patients demonstrated.

The response seen will basically set the tone for the rest of the trial.

If it’s complete response across the board, that’s incredible news, and the company will soar come data day. If it’s partial or stable, that’s not bad, but not great, and the response will probably come down to how many patients experienced said response, and to what degree.

We don’t know exactly when GTXI intends to get the numbers in the hands of investors, or the degree of detail in to which the company plans to report, but there’s probably a few week delay while it collates the data and runs it through its database. The company gave guidance of late 2016, so we’re putting this alongside our three week delay estimate and looking at the first or second week of December.

One to watch.