GSK has spent most of 2026 as the unloved corner of Big Pharma. Shares closed at $49.51 on October 16, well below the recent high close of $59.52 set in February 2026. While AstraZeneca compounded double-digit growth and Merck’s Keytruda empire kept expanding, GSK ground along at a price-to-earnings ratio of roughly 15, against a market average nearly three times that. The combination of a modest year-to-date price increase, an earnings-growth forecast in the mid-single-digit range, and a P/E ratio less than half the broader market average gave GSK the profile of a defensive, income-oriented stock rather than a high-volatility growth play.
That profile got its first genuine challenge on Monday, October 19, 2026, when the FDA granted accelerated approval to Jemperli (dostarlimab) for a use that has no precedent in oncology: the first immunotherapy authorized for adults with stage II and III MSI-H/dMMR locally advanced rectal cancer. The agency’s own framing was blunt. Certain patients with this subtype may now avoid chemotherapy, radiation, and surgery entirely.
Investigator-assessed data showed 68% of evaluable patients achieved sustained clinical complete responses at 12 months, and in an exploratory analysis, 76% of evaluable patients had no evidence of cancer one year or more after treatment. No disease recurrences have been reported among responders after a median follow-up of more than two years. Those are not incremental numbers. They are the kind of results that rewrite standard of care.
The realistic market size, though, requires honesty. MSI-H/dMMR tumors constitute only about 5% to 10% of rectal cancers, of which there are an estimated 49,990 new cases in the U.S. in 2026. That caps the addressable pool at perhaps 2,500 to 5,000 newly eligible American patients annually. GSK has told investors it is targeting £2 billion-plus in peak Jemperli sales. Jemperli already generated £861 million in 2025 revenue, making it the company’s top-selling oncology product. This label adds fuel, not a new engine.
The competitive picture deserves scrutiny. Both Jemperli and Merck’s Keytruda hold tumor-agnostic FDA indications covering MSI-H/dMMR solid tumors in the advanced or metastatic setting, including colorectal cancer. Keytruda does not yet have this specific stage II or III locally advanced rectal label, which gives GSK a narrow window of exclusivity. Whether oncologists adopt Jemperli broadly, or default to the more familiar pembrolizumab off-label, is an open question that prescription data over the next two quarters will answer.
The near-term calendar is dense with catalysts. Q3 results arrive October 28, preceded by a PDUFA goal date for a regulatory decision on hepatitis B treatment bepirovirsen on October 26 and an oncology investor briefing on October 27. Analysts are projecting Q3 EPS of $1.45, after GSK beat consensus in each of the prior two quarters. Full AZUR-1 interim data are slated for the European Society for Medical Oncology Congress, which runs October 23 to 27, 2026, the same week, giving the oncology investor briefing fresh content to work with.
A compressed catalyst calendar rewards investors who understand how pharma earnings beats get priced. Bristol-Myers showed how a growth portfolio inflection can shift the narrative even when legacy headwinds are already built into guidance.
The investment case for GSK today is not a momentum story. Jefferies maintained its Buy rating on October 19, 2026, but the stock trades at a meaningful discount to both sector peers and intrinsic value estimates. A first-and-only cancer label that spares patients surgery is a genuine commercial and scientific achievement. Whether it is enough to close the valuation gap against AstraZeneca or Merck depends on how aggressively Jemperli captures the rectal cancer market and whether the broader pipeline delivers. For investors willing to own a laggard with a fresh catalyst and earnings in eight days, GSK offers a more interesting risk-reward today than it has all year.
