An increase in platelets in a routine blood test may indicate the need to investigate occult cancer.

Two published studies (one from the UK and a more recent one from Canada) seem to point in the same direction: the connection between thrombocytosis (increased platelet count) and the presence of cancer.

Some tumors, which course with few signs and symptoms, and thus tend to be diagnosed later, are those most likely to be associated with thrombocytosis (platelet count > 450,000/mm³).

This most recent study, which involved analyzing more than three million medical records in Canada, showed that the presence of thrombocytosis was associated with an increased risk of some types of cancer over up to five years. A routine complete blood count may have a greater impact than previously thought.

Laboratory data from January 1, 2007, to December 31, 2017, from this population were evaluated in this retrospective study that included adults 40 to 75 years of age. These study participants had normal platelet counts in the two years before this assessment and had no history of cancer.

A finding of thrombocytosis (platelet count > 450,000/mm³) was associated with a greatly increased risk of some cancers within up to five years. This Canadian study reports that the probability of a cancer diagnosis was increased by 2.7 times in two years in the face of a high platelet count. The extremely higher risk was for ovarian cancer and then pancreatic cancer and cervical cancer.

Of the 3,386,71 Ontario residents with a blood cell count result, 53,339 (1.6%) of them had thrombocytosis and a previous normal platelet count, and of those with thrombocytosis, 70% were women.

In this Canadian population with a diagnosis of thrombocytosis, as found on routine examination, including a blood cell count, and who had a normal platelet count in the previous two years, thrombocytosis was associated with an increased risk of cancer.

Patients with thrombocytosis were more than 4 times more likely to be diagnosed with lung cancer when compared with patients with normal platelet counts.

Although it was not definitively demonstrated in this study, a complete blood count may indicate an earlier investigation/screening for early-stage cancer, allowing an earlier diagnosis of this cancer and, certainly, a more favorable evolution for these patients.

Some tumors, such as breast, prostate, and thyroid, are not usually associated with thrombocytosis.

The other study carried out in the United Kingdom showed similar findings: the association between cancer incidence and platelet count. These investigators, however, indicate that a group of thrombocytosis patients over age 65 had no symptoms suggestive of cancer in the 21 days before the high platelet count examination. These data may suggest that routine blood tests with thrombocytosis may indicate the presence of occult tumors.

A total of 1098 of 9435 men with thrombocytosis were diagnosed with cancer (approximately 11.6%) compared with 106 of 2599 men without thrombocytosis (approximately 4.1%). And a total of 1355 of 21 826 women with thrombocytosis developed cancer (about 6.2%) compared with 119 of 5370 women without thrombocytosis (about 2.2%). Thus, there was an increased risk of cancer, 18.1% in men and 10.1% in women, when a second increased platelet count occurred within 6 months. Lung and colorectal tumors were the most commonly diagnosed with thrombocytosis. One-third of patients with thrombocytosis and lung or colorectal cancer had no other symptoms indicative of a malignant tumor.

In this population, lung cancer and colorectal cancer were the most commonly diagnosed with thrombocytosis.

Admittedly, cancer is one of the leading causes of death in developed countries. Usually, the diagnosis of cancer occurs after the development of symptoms, and the definitive diagnosis, after referring the patient to a specialist, is established by a biopsy.

The delay in the early diagnosis of cancer, that is, a diagnosis in already symptomatic patients, certainly brings some degree of harm to these patients.

Only recently has increased platelet count or thrombocytosis been recognized as a potential diagnosis of possible cancer. Thrombocytosis may be present in 1.5 to 2.2% of a population aged ≥ 40 years. Some studies have previously reported associations between the finding of thrombocytosis in primary care and a future diagnosis of lung, renal, uterine, and colorectal cancer. Other studies have not considered thrombocytosis as a predictive factor for pancreatic, breast, ovarian or gastroesophageal cancer.

The question that persists among investigators is whether or not platelet counts can be considered a new cancer screening tool. Possibly, the routine platelet count in asymptomatic patients may indicate in the future whether it will be a valuable weapon for the early identification of cancer.

However, the UK study showed that patients with high normal platelet counts (> 326,000/mm³) were 4 to 5 times more likely to have lung cancer.

Thus, everything seems to indicate that an unexplained increase in platelet counts, even within normal reference values, deserves attention.

References

• Medscape — 13 de outubro de 2021.
• Bailey SER et al — Br J Gen Pract, 2017
• Giannakeas V et al — JAMA Network Open, 2021.