Here's what happens when a small biotech company reports promising cancer drug data: investors get excited, and the stock goes up. A lot. That's exactly what happened with CytomX Therapeutics Inc. (CTMX) on Monday, as shares jumped more than 66% in premarket trading after the company released positive Phase 1 expansion data for its experimental cancer drug.

The drug in question is called varsetatug masetecan (or Varseta-M for those of us who prefer shorter names), and it's what's known as a PROBODY ADC—a type of targeted cancer therapy designed to attack tumors while sparing healthy tissue. The latest data showed the drug is working in patients with metastatic colorectal cancer who have already tried other treatments.

Positive Data For Colorectal Cancer Patients

Let's talk numbers, because that's what really matters here. At a dose of 10 mg/kg given every three weeks, 32% of patients saw their tumors shrink. At a slightly lower dose of 8.6 mg/kg, the response rate was 20%. Perhaps even more impressive: across all the doses tested (ranging from 7.2 to 10 mg/kg), 88% of patients achieved disease control—meaning their cancer either shrank or stopped growing.

For patients facing late-stage colorectal cancer, that's meaningful progress. The estimated progression-free survival at the higher dose was 7.1 months, which gives patients more time without their disease worsening.

On the safety front, the most notable side effect was diarrhea, with a Grade 3 (serious) rate of 10% in ongoing dose optimization cohorts. The company says the safety profile appears manageable, which is biotech-speak for "we think we can work with this."

CytomX Therapeutics Development Strategy

So what's next? CytomX has decided to focus on those two doses—8.6 mg/kg and 10 mg/kg—for further evaluation. They're continuing to optimize dosing using something called AIBW dosing (adjusted ideal body weight, for the curious) and updating how they manage side effects.

Interestingly, at even higher doses (11 mg/kg and 12 mg/kg), the response rate was 30%, but the company isn't expanding those for further evaluation. Sometimes in drug development, more isn't better—it's about finding the sweet spot between effectiveness and tolerability.

The company is planning to talk with the FDA about designing a registrational study, which is the big trial that could eventually lead to approval. They've also started a Phase 1 study combining Varseta-M with Avastin (bevacizumab), and they expect to begin a larger Phase 1b/2 study combining the drug with both bevacizumab and chemotherapy by the end of 2026.

CytomX Therapeutics Stock Performance And Technical Signals

Now, about that stock move. CytomX has been on an absolute tear over the past year, with shares up a staggering 639%. That's the kind of return that makes biotech investors both excited and nervous.

Technically speaking, the stock is trading 39% above its 20-day simple moving average and 59% above its 100-day average, which suggests strong momentum. The RSI (Relative Strength Index) sits at 40.59, which is neutral territory—neither overbought nor oversold. But the MACD (Moving Average Convergence Divergence) shows a value of -0.1367, below its signal line of -0.0651, indicating some bearish pressure.

What does all that technical jargon mean? Basically, the stock has shown incredible strength but might be due for a pause or pullback. Key resistance sits at $6.50, while support is at $5.00.

Analysts seem optimistic despite the technical mixed signals. The stock carries a Buy rating with an average price target of $7.25. Recent analyst moves include Guggenheim maintaining a Buy rating with a $10 target, Cantor Fitzgerald raising its target to $10, and Barclays also raising its target to $10.

At the time of publication, CytomX Therapeutics shares were up 66.45% at $7.78, trading at a new 52-week high. For a mid-cap biotech company, that's the kind of day that makes headlines—and gives hope to patients waiting for new treatment options.