The S&P/ASX 300 Index (ASX: XKO) is struggling today, but that's not holding back ASX 300 healthcare stock Immutep Ltd (ASX: IMM).

Shares in the clinical-stage biotech company closed Friday at 29.5 cents. In morning trade on Monday, they are changing hands for 30.5 apiece, up 3.4%. This sees the ASX 300 healthcare stock up 33.6% since hitting a one-year closing low of 22.5 cents on 16 April.

For some context, the ASX 300 is just about flat today and up 7.8% since 16 April.

Today's outperformance for Immutep shares follows on promising clinical cancer treatment trial results.

Here's what's happening.

ASX 300 healthcare stock leaps on cancer treatment progress

The Immutep share price is marching higher after the company reported that its Phase II trial evaluating its eftilaginod alpha (efti) treatment in combination with radiotherapy plus Merck & Co's anti-PD-1 therapy KEYTRUDA (pembrolizumab) in the neoadjuvant setting for resectable soft tissue sarcoma (STS) has met its primary endpoint.

The ASX 300 healthcare stock reported that the novel combination significantly exceeded the study's prespecified median of 35% tumour hyalinization/fibrosis versus 15% for historical data from radiotherapy alone in patients with resectable STS.

According to the release, tumour hyalinization/fibrosis is an early surrogate endpoint at the time of surgical resection that has been associated with improved overall survival and recurrence-free survival for STS patients.

STS is an orphan disease with high unmet medical needs and a poor prognosis for patients. According to the American Cancer Society, the number of new STS cases in 2025 in the United States is around 13,520, with approximately 5,420 deaths.

The trial's investigators at the Maria Skłodowska-Curie National Research Institute of Oncology, the national reference centre for STS in Poland, intend to present detailed results from the latest study at an upcoming medical meeting.

What did management say?

Commenting on the clinical trial results helping boost the ASX 300 healthcare stock today, medical oncologists Katarzyna Kozak and Paweł Sobczuk at MSCNRIO, said:

It is very encouraging to see the chemotherapy-free combination with efti far exceed the ambitious target we initially set for the trial's primary endpoint in resectable soft tissue sarcoma.

These results support our belief that efti's activation of antigen-presenting cells, and in turn a broad adaptive and innate immune response, helps transform the immunosuppressed tumour microenvironment of soft tissue sarcomas leading to strong anti-cancer efficacy.

The oncologists added, "There remains a very high unmet need in this aggressive orphan cancer indication, and we look forward to presenting detailed results at a medical meeting later this year."

Immutep share price snapshot

Despite the big lift since April's one-year lows, with today's intraday boost factored in, shares in the ASX 300 healthcare stock remain down 33% since this time last year.