Cancer rates in the US continue their long decline in 2016, according to a new report, though the disease remains the second leading cause of death around the country.

Deaths caused by cancer have dropped 23% since 1991, according to an American Cancer Society report released on Thursday.

The overall decline in cancer deaths for the past two decades is largely attributed to improved screenings for breast cancer and prostate cancer, as well as a decline in smoking.

The annual report estimates that 1.6m new cancer cases will be diagnosed in 2016, the equivalent of about 4,600 new diagnoses each day. The authors expect 595,600 people to die from cancer this year, or 1,600 people per day.

The statistics are complicated by separate but encouraging data. Cancer remains the leading cause of death in 21 states, largely because heart disease deaths dropped significantly in those states.

Doctors are diagnosing thyroid cancer more rapidly than any other cancer, but this is because advanced imaging techniques have made it easier to find small thyroid cancers that are not actual threats.

Dr Michael Tuttle, an attending physician at Memorial Sloan Kettering, said that for “the last million years” no one knew that about 10-15% of the population has thyroid cancer. But in most cases, these are small cancers that were never going to harm the patient.

“There is no question, the data is the data, we’re making more diagnoses,” he said. But most of those diagnoses are “very small thyroid cancer and many of us are questioning the clinical significance of that thyroid cancer”, he added.

Tuttle noted that larger forms of thyroid cancer are also being diagnosed at increasing rates, but still at a much slower rate than the low-grade ones.

The report’s projections for cancer rates in 2016 are based on government data from 2012, and the ACS warns that they will “not be used to track trends over time”. This is because researchers cannot predict some factors, such as how improved detection strategies have changed thyroid cancer diagnoses.

But the disease is still one of the most common causes of death in the US, alongside heart disease, cardiovascular disease, suicide and car crashes. For males and females aged 40 to 79, cancer was the leading cause of the death in the US in 2012.

And though the overall picture shows a steady decline, there are still significant disparities in who has access to cancer screenings and treatment.

Black men have the highest overall cancer incidence across five population groups, and were two and a half times more likely to die from stomach or prostate cancer than white men, the report found.

“We do know that minorities in general have access to lower-quality cancer care to begin with and lower volume [of] specialists, so that has an impact on your survival,” said Dr Gina Villani, CEO and president of the Ralph Lauren Center for Cancer Care and Prevention.

Villani, the former chair of the American Society of Clinical Oncology’s health disparities committee, said that clinical trials also lack diversity, which many people believe is already causing a problem for breast cancer treatment.

Although black women and white women are diagnosed with breast cancer at the same rate, black women die from the disease at a higher rate, according to the report.

“The gap between black women and white women has gotten wider over time and that reflects who gets access to quality treatment,” said Linda Goler Blount, an epidemiologist and CEO of Black Women’s Health Imperative, an organization that promotes women’s health.

The ACS report said that this disparity is partially caused by obesity and childbearing patterns, but Blount believes it also comes from the medical community not collecting enough information about black women’s health needs.

The ACS said in October that women should start annual mammograms later in life than previously recommended, at age 45 instead of 40. But black women tend to get breast cancer at a younger age than white women, Blount said.

She and other advocates believe that raising the recommended age to begin mammogramscould increase women’s rates of death.

“We know ethnicity plays a role, what part of the country you come from does play a role in your disease expression,” she said. “So we really do need to devote research dollars into the role of ethnicity, and the role of the lived experience that certain populations in this country have in their disease expression.”