Dr Lynn Turner, director of research at Edinburgh-based charity Worldwide Cancer Research, said the news brought into “sharp focus” concerns that Covid-19 had sidelined work in many other fields.
Cancer Research UK said if the charity did not find further support, it would have to make research budget cuts for the next four to five years.
A spokesperson for Chest, Heart and Stroke, which supports people across Scotland with those conditions, said a year of lockdowns may have had a negative impact on people’s health, leading to an increase in risk for heart disease and stroke.
“During lockdown, people haven’t been as active, their diet may have changed and stress levels have been higher,” the spokesperson said.
"All these things can increase the risk factors for heart disease and stroke.”
He added: “The knock on health impacts of Covid are likely to be felt for years to come and we will need to redouble our efforts to find solutions to the complex problems it has created.”
It comes as figures from National Records of Scotland this week showed March was the first month since October 2020 that Covid-19 was not the leading cause of death.
Instead it was number five, behind dementia/Alzheimer’s, heart disease, and other circulatory and respiratory diseases.
Dr Turner said: "The recent statistics which show Covid-19 is no longer the leading cause of death in Scotland marks a welcome milestone in the fight against the virus, and a declining trend that we perhaps couldn’t have imagined at the turn of the year.”
She added: “The shift in the landscape, however, brings into sharp focus our concern about the impact of the ongoing pandemic on cancer, specifically cancer research, and what that means for those living with the disease.
"The long-term consequences may not be visible now, but that doesn’t mean they aren’t there.”
Graeme Sneddon, spokesperson for Cancer Research UK in Scotland, said: “The pandemic has slowed us down by hitting our income. If we don’t find further financial support, Cancer Research UK will regrettably need to make major cuts to our research budget every year for the next four to five years.”
He said this would mean a research funding cut of up to £150 million across the UK.
“This situation would leave scientists with fewer options to make those crucial discoveries which lead to better treatments,” he said.
Dementia and Alzheimer’s accounted for 12 per cent of deaths last month, while 11 per cent were attributed to ischaemic heart disease.
In February, Covid-19 accounted for 31 per cent of deaths, while in January that figure was 18 per cent.
Covid-19 is still the leading cause of death across the whole year since March 2020.
It comes as new figures from the Office for National Statistics (ONS) suggest one of the smallest annual increases in UK population seen so far in the year to June 30, at 0.5 per cent.
These provisional figures reflect a higher number of deaths, the ONS said, as well as a continued decrease in birth rates and higher levels of net migration.