The gynaecological disorder occurs when tissue similar to the lining of the uterus, or endometrium, migrates outside of the womb, generally to the fallopian tubes, ovaries and tissue around the uterus.
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The resulting symptoms are debilitating for an estimated 200mln women worldwide and the condition represents one of the biggest health issues for females of reproductive age, the company said.
The market for drugs treating the condition is expected to grow to US$1.91bn by 2023.
"This US patent grant is excellent news for VAL301 and for our opportunity of trying to address this little known, but hugely widespread and debilitating chronic illness that affects a very substantial number of women around the world,” said chief executive, Dr Satu Vainikka.
“New targeted treatments with minimal side effects are needed, particularly when considering the target patient group - young women of child-bearing age.”
In early morning trading, ValiRX shares were up 10% at 2.75p.
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