Roche's (RHHBY) struggle to perfect its potential blockbuster haemophilia treatment has highlighted the intensity of competition in a $10 billion market already crowded with rivals such as Pfizer (PFE - Get Report) , Bayer (BAYRY) , and Shire (SHPG) .

The market for haemophilia drugs - in order to treat patients who suffer from bleeding for longer periods than normal due to disorder in blood clotting abilities - is set to grow at a compound annual rate of more than over 5% over the next few years, according to Grand View Research. 

The Basel, Switzerland-based Roche, which has been conducting clinical trials on emicizumab, or ACE910, said in a statement obtained by TheStreet Thursday that four patients reported serious adverse events as a result of treatment. Emicizumab is aimed patients suffering from haemophilia A, a more common form of the disorder than types B and C.

Roche added that all these cases had involved "concomitant use of multiple doses of a bypassing agent with emicizumab while treating a breakthrough bleed; in some cases the bypassing agent at doses exceeding the recommended labelled doses."

Roche AG shares fell 0.74% in Zurich Thursday, changing hands at Sfr222.60 each and extending the year-to-date decline to nearly 20%. 

Rivals are bracing for the outcome of the ongoing trial for Roche's emicizumab expected at the end of the year, as the drug is likely to change the way haemophilia A patients are treated, enabling them to reduce the frequency they need to receive treatments to just once a week.

Shire Plc (SHPG) , a direct competitor in the haemophilia market, saw its stock jump 4% in London following Roche's statement before paring gains to 2.5% and changing hands at 4,539 pence each.

Earlier this week, the Ireland-based biopharmaceutical company, which had acquired Baxalta in June 2016 primarily to take on its haematology business, faced a 5% drop in the sales of haemophilia products in the third quarter. Shares plunged following the earnings announcement. 

Pfizer may be another company nervous about new products. Last week, the New York-based group reported a 8% revenue increase in worldwide ReFacto drug sales, its haemophilia A line, in the nine months to October 2.  Sales in Europe, however, have fallen. 

Bayer is another player that is deep in the haemophilia A drug market. In December 2015, the company gained approval from European authorities to market bay 81-8973. Meanwhile, another drug Damoctocog alfa pegol is now in Phase III trial stage.

The global haemophilia market, valued at $9.3 billion in 2015, is expected to expand at a CAGR of 5.6% through 2024, according to Grand View Research. Market research firm Technavi estimates the growth at over 5% between 2016 and 2020.

Roche added to the Thursday statement that the adverse events by the four patients had been resolved, and that they had no impact on the timing of the outcome of the study to come out at the end of this year.

Other players involved in the haemophilia drug market include CSL Behring (CSLLY)   and Novo Nordisk (NVO - Get Report) .

Until now, Roche's emicizumab, created by Japan's Chugai Pharmaceutical and being co-developed by the Swiss player, had shown positive clinical trial results.

In May, Chugai announced that a Phase I study conducted on 18 patients showed "a clinically acceptable safety profile and a potential benefit" for haemophilia A patients.

In July, Roche said a long-term follow-up data from a Phase I/II study showed that emicizumab resulted in "promising safety and prophylactic efficacy for people with severe haemophilia A."