A 73-year-old man comes to the office for follow-up. He was diagnosed with chronic lymphocytic leukemia (CLL) 3 years ago when routine laboratory testing revealed a markedly elevated leukocyte count. He feels well. On examination, he has stable lymphadenopathy. He has been reading about management options should his CLL progress and inquires about an experimental drug that selectively binds malignant lymphocytes. The drug has been shown to significantly prolong survival in patients with stage 3 and 4 CLL, without curing the malignancy. If this new drug were widely used, what changes would be expected in the number of incident and prevalent cases of CLL?

Question

A 73-year-old man comes to the office for follow-up.  He was diagnosed with chronic lymphocytic leukemia (CLL) 3 years ago when routine laboratory testing revealed a markedly elevated leukocyte count.  He feels well.  On examination, he has stable lymphadenopathy.  He has been reading about management options should his CLL progress and inquires about an experimental drug that selectively binds malignant lymphocytes.  The drug has been shown to significantly prolong survival in patients with stage 3 and 4 CLL, without curing the malignancy.  If this new drug were widely used, what changes would be expected in the number of incident and prevalent cases of CLL?

Quizplus · Accepted Answer

Incident cases represent new cases diagnosed in a given period of time. Prevalent cases are the total number of cases (both old and new) at a particular point in time. For a non-transmissible condition such as chronic lymphocytic leukemia (CLL), the number of incident cases will not be changed by any kind of treatment because the disease has already developed when the treatment is started (and treatment of existing patients will not prevent new patients from developing CLL). Any treatment that prolongs survival but does not cure the disease will increase the number of prevalent cases due to an increase in the number of afflicted (but still living) individuals over time. Differences in terminology may lead to confusion. Incident cases and prevalent cases are often referred to as simply "incidence" and "prevalence." Incidence can also represent the number of new cases divided by the population at risk over a period of time and can be converted into a rate (eg, annual incidence per 10,000 population). Prevalence typically refers to point prevalence (total number of cases at a particular point in time) as opposed to period prevalence (over a period of time). The specific meaning is often clear from the context. Educational objective: Incident cases represent new cases diagnosed in a given period of time. Prevalent cases are the total number of cases (both old and new) at a particular point in time. Any treatment that prolongs survival but does not cure the disease will increase prevalence due to an increase in the number of afflicted (but still living) individuals over time.

A 73-Year-Old Man Comes to the Office for Follow-Up