The latest cuts lift the retailer's total number of price reductions over the past year to more than 10,000.
Metro said it is assessing the wider implications of the decision for the company.
The Warsaw-listed discounter's earlier guidance was growth above 50% in the year to 30 September 2026, against a restated FY25 base of €234m.
The partnership will bring Sephora shop-in-shops to 100 M&S locations across high streets and retail parks nationwide.
A review found that many of the supermarket chain’s pharmacy sites were financially unviable.
The agreement, which extends to 2036, carries an approximate annual value of £25m.
