By Mrinalika Roy

Oct 18 (Reuters) - AstraZeneca ( AZN ) and Daiichi

Sankyo's ( DSKYF ) drug Enhertu has shown strong results in two

pivotal studies in the early stage of a certain type of breast

cancer, according to data announced on Saturday.

The findings from both trials, presented at the European

Society for Medical Oncology Congress, indicate that the drug,

currently used for advanced stages of certain cancers, could

advance toward curative treatment.

In one late-stage study, Enhertu cut the risk of invasive

disease recurrence or death by 53% compared with Roche's

Kadcyla, in patients with high-risk early HER2-positive breast

cancer that persisted after surgery and initial therapy.

Three years after treatment, 92.4% of patients on Enhertu

were alive and disease-free, versus 83.7% on Kadcyla.

Enhertu belongs to a class of medicines called antibody-drug

conjugates (ADC), also known as "guided missiles", for its

ability to target cancer cells specifically, while sparing

healthy cells, unlike conventional chemotherapy.

HER2-positive breast cancer accounts for about 15% to 20% of

all breast cancers.

In a second study, patients treated with Enhertu before

surgery achieved a 67.3% pathologic complete response rate,

compared with 56% for standard chemotherapy and experienced

fewer severe side effects.

For AstraZeneca ( AZN ), the results not only strengthen Enhertu's

commercial potential but also validate its broader ADC strategy.

"This vision we have for antibody drug conjugates to

displace chemotherapy in multiple different settings is

demonstrated," said Susan Galbraith, AstraZeneca's ( AZN ) executive

vice president of oncology R&D.

The sentiment was echoed by Ken Keller, global oncology head

at Daiichi Sankyo ( DSKYF ) - "Any place where chemotherapy is active, we

ask whether our DXd ADCs can do more. That will guide our

choices."

The companies are now advancing a broad regulatory program

for Enhertu, and Keller believes the biggest constraint will be

the time it takes to get regulatory approval.

"I am not worried about the adoption", Keller said, adding

that the focus should be on ensuring countries can afford and

reimburse the cost of the drug.

Combined sales of Enhertu by both companies reached $3.75

billion last year. It is currently approved in more than 75

countries for several types of cancers, including specific types

of breast, non-small cell lung and gastric cancers.