These were the best performing ASX biotech shares in September

The S&P/ASX 200 index (ASX: XJO) has started the week on a downward trend, trading 0.36% lower today at 7251.1 points.

At the same time, the S&P/ASX 200 Health Care index (XHJ) has also slipped 0.36% into the red from the opening of trade.

Aside from this, these ASX biotech shares have been a standout amongst their healthcare peers in September.

Read on to see how each performed last month.

Imugene Limited (ASX: IMU)

Immunotherapy company Imugene had a month full of momentum that propped its share price from 41.5 cents to 48 cents across the month of September.

Investors enjoyed the gains on a backdrop of positive results from the company's HER-Vaxx immunotherapy candidate.

HER-Vaxx is being investigated in several clinical trials, and in September, positive readouts from a Phase 2 trial showed the label to be potentially effective as a kind of therapy in HER-2 gastric cancer.

Then came further good news on the drug candidate that it had received patent approval in Japan over its method of consumption and use.

Imugene was also added to the S&P/ASX 300 Index last month, indicating the growth of this ASX biotech share in recent times.

In the last year alone, Imguene shares have soared over 720% to date and climbed 16% in September.

Clinuvel Pharmaceuticals Limited (ASX: CUV)

Shares in global biopharma company Clinuvel Pharmaceuticals climbed from $36.50 to $42.86 in September, a 17.5% monthly gain.

Clinuvel shares popped when the company reported its FY21 earnings on 26 August, where they were trading at $29 and change just prior to this.

This momentum carried through the month of September, as investors appeared to have favoured the company's 43% year on year (YoY) gain in revenue and 63% YoY increase in profit after tax.

Shareholders will also enjoy a 2.5 cents dividend from the company from its FY21 results, which is flat with the year prior.

Clinuvel's share price performance last month brings its gain for the year to 84%, well ahead of its benchmark indices.

Starpharma Holdings Limited (ASX: SPL)

The Starphama Holdings share price rallied across the month of September from $1.20 to $1.33, at one point closing at a high of $1.475 on 27 September.

The ASX biotech share had a choppy month after investors started to buy it in droves after Starpharma released its FY21 earnings on 26 August.

Whilst the company saw a number of headwinds from its FY21 operations, including a 67% down-step in revenue, investors appeared to look past the company's financials.

This was backed by the US Patents and Trademarks Office (USPTO) approving a patent for the company's DEP cabazitaxel label, which covers DEP dendrimer coupled with multiple cabazitaxel drug molecules, with a novel mechanism of action.

This particular hypothesis is being tested in over 40 patients in a Phase 2 clinical trial, for the potential treatment of various cancers.

Despite the positive month, it has been a difficult year for the Starpharma share price, having posted a loss of 22% since January 1, and over 18% this past 12 months.

Collectively, these ASX biotech shares have outperformed their benchmarks in September, and awarded investors with healthy gains.