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* Drug candidates are in class known as PARP inhibitors
* Companies to discuss results with healthcare regulators
(Adds details on patient subgroup, sales estimates)
By Ludwig Burger
BARCELONA, Sept 28 (Reuters) - GlaxoSmithKline and
AstraZeneca both reported trial results that will likely
make their competing drugs available to a wider group of ovarian
cancer patients, possibly helping GSK catch its rival in a
highly contested drug class.
The two said separately on Saturday their drug candidates -
in a class known as PARP inhibitors - staved off the return of
metastasized ovarian cancer in women who had responded to
initial standard treatment, reducing the risk of a relapse.
AstraZeneca and its U.S. development partner Merck & Co
said their Lynparza drug cut the risk of the cancer
progressing again by 41%. The figure was 38% for GSK's drug.
The companies said they would discuss the results with
healthcare regulators with a view to a wider label.
Analysts have seen AstraZeneca and Merck's Lynparza in the
lead with an average sales estimate of $3.1 billion for 2023.
GSK's Zejula is seen achieving about 870 million pounds ($1.1
billion) in revenue that year.
But different trial settings will make it difficult to
predict how physicians will weigh up the two drugs.
While the Lynparza trial worked on the assumption that
patients get an initial treatment of chemotherapy plus Roche's
Avastin, the trial with GSK's Zejula included only
patients who had initially gone through chemotherapy only.
AstraZeneca argues that more than half of advanced ovarian
cancer patients in developed countries already get Avastin, with
the rate increasing, while GSK says concerns about side effects
may speak against the Roche drug.
Both companies, which are competing to burnish their
oncology credentials, showed that not just the small group of
women with mutated BRCA genes can benefit as the results also
covered the full variety of ovarian cancer.
Many cancer cells have a limited ability to make DNA repairs
during cell division, as healthy cells would. This feature makes
tumours genetically volatile and helps them develop resistance
to treatment over time.
GENETIC MUTATIONS
Drugmakers try to use that to their advantage with PARP
inhibitors, which block what is left of the DNA repair mechanism
so cancer cells fail to replicate. Mutated BRCA genes make the
DNA repair particularly weak, which is why PARP inhibitors have
been approved already for that subgroup.
Both trials showed benefit in using Zejula or Lynparza also
in tumours with a wider range of genetic mutations that hamper
DNA repairs, grouped together under the term homologous
recombination deficiency (HRD).
But in a patient subgroup with tumours where the DNA repair
was still intact, GSK appears to make headway over its rivals.
That group, which according to GSK accounts for about half
of ovarian cancer cases, showed a reduction in the cancer
relapse risk by 32%, when given Zejula.
In the Lynparza trial, however, there was no meaningful
benefit in that cohort. But reliable tests on HRD have yet to
become widely available.
"We know now we can use PARP inhibitors in the first-line
setting beyond women with BRCA mutations," said Susana Banerjee,
an oncologist at the Royal Marsden NHS Foundation Trust in
London, who discussed the results at an ESMO press conference.
"I think the key question really is, what about patients
that don't have HR deficiency?" Banerjee added.
Zejula was the lead compound of U.S. cancer specialist
Tesaro, which GSK acquired for $5.1 billion in December.
Other approved PARP inhibitors, Pfizer's Talzenna and Clovis
Oncology's Rubraca, are seen as further behind in terms
of future revenue prospects. Abbvie is testing an
experimental compound called veliparib.
($1 = 0.8039 pounds)
(Reporting by Ludwig Burger
Editing by David Holmes)
