Turkey's main BIST-100 share index ​rallied some 23% in the ⁠last month, the fourth largest gain in more than 20 years, stoked by some breakaway stocks including Kiler Holding and ‌index leader Aselsan that produced returns well above the rest.

The index is up 43% over the past 12 months and some of the stocks with ​the biggest rises have had an outsized influence: Kiler and Aselsan alone regularly account for nearly a quarter of the index's daily move, according to ​LSEG ​data and Reuters calculations.

Kiler briefly emerged as the second most valuable company listed on the Istanbul exchange at the end of a near four-month rally, when it reached a market capitalization of 1.1 trillion lira ($24.4 billion) on February 4, jumping ⁠above blue chips like industrial conglomerate Koc Holding.

After a plunge of 35% in the past two weeks, the company, which operates across construction, energy, transport, retail and industrial sectors, still ranks third-largest in the main index as of Tuesday's close, far above its $1 billion capitalization a year ago, according to Reuters calculations.

Founded in 2007, Kiler trades with a price-to-earnings ratio above 460, compared to an industry ​median of around 10, according ‌to LSEG data. ⁠In the first nine ⁠months of last year, Kiler's revenues stood at 5 billion lira ($114 million), dwarfed by Koc Holding's 1.3 trillion lira ($29.6 billion).

Market observers say low liquidity, ​speculative fund positioning and inclusion in the bourse's top indices drove Kiler stock higher.

On Tuesday, MSCI said ‌it had reversed its decision this month to add Kiler to its global ⁠standard indices after receiving feedback from market participants citing uncertainty over the company's free-float level, leading to a 10% loss on Wednesday.

MSCI said it will conduct further analysis and retain Kiler's shares in MSCI Turkey Small Cap Index. Aselsan, Turkey's largest defence company by revenues and its most valuable listed stock, has risen 272% in the past 12 months, delivering 204% returns in dollar terms and outperforming Europe's defence sector index, which rose 73% in the same period. The company is valued at around 1.4 trillion lira ($32.6 billion), with a price-to-earnings ratio of around 60 against an industry median of around 30. Aselsan stock has been supported by an uptick in orders as well as retail interest in defence stocks. Chief Executive Ahmet Akyol said annual new export orders passed the $2 ‌billion threshold for the first time last year, with export deliveries around $1 billion.

According to its 2025 ⁠full-year report released on Tuesday, Aselsan increased its net profit to 29.95  billion lira ($683.2  million), ​about 50% above last year.

On the other hand, some stocks have suffered heavy losses, including consumer electronics maker Vestel Elektronik , which fell almost 50% over the past year.

Among companies listed on Istanbul's broader index, which is up 52% year-on-year, several have surged more than tenfold. Once ​a small-cap, Tera ‌Yatirim is up more than 2,600% year-on-year, with around a 100x increase in market cap at $3.7 billion.

It ⁠is followed by Hedef Holding, which is up ​more than 1,500%. ($1 = 43.8621 lira)

(Reporting by Mirac Eren Dereli; Editing by Can Sezer, Jonathan Spicer and Aidan Lewis)