The phrase "a subject of growing" is correct and usable in written English.
It can be used when discussing topics or issues that are increasingly gaining attention or importance over time.
Example: "Climate change is a subject of growing concern among scientists and policymakers alike."
Alternatives: "an area of increasing" or "a topic of rising".
It's even a subject of growing interest in Middle America.
Greenway planning and design is now undoubtedly a subject of growing significance in Portugal.
The separation of secondary oil in water dispersions in packed-bed coalescers has become a subject of growing interest.
The role of charity and philanthropy in development is a subject of growing interest within the global aid community.
For the last two decades the Internet of Things (IoT) has been a subject of growing global interest.
This is especially remarkable in monitoring water- and wastewater-quality parameters, currently a subject of growing concern throughout the world.
In recent years, MDMA has been a subject of of growing interest to clinicians.
Vibration energy harvesting has been a research subject of growing interest over the past few years, and is envisaged as a remedy to the unsatisfactory battery issue in low-power electronic devices.
The first sentence of the story refers to "the problem of homosexuality," which is, according to a later sentence, "the subject of growing concern of psychiatrists, religious leaders and the police".
Apple has not indicated whether it is working on the device, but the possibility of an "iWatch" has been the subject of growing speculation since reports surfaced earlier this year that Apple had a team working on a "wearable computing" product – a field that chief executive Tim Cook called "profoundly interesting".
The future of Caspian beluga sturgeon, a bony fish whose armor-plated body can grow as long as 15 feet and weigh more than a ton, has been the subject of growing concern since the disintegration of the Soviet Union and the ensuing competition among the fishermen of Azerbaijan, Russia and Kazakhstan for primacy in sturgeon harvesting in the Caspian Sea.
