A retrospective study published in Asian Pacific Journal of Cancer Prevention found that season of recurrence, but not season of diagnosis, is significantly associated with survival outcomes in epithelial ovarian cancer patients.
Epithelial ovarian cancer (EOC) is cancer that begins in the ovaries and is the eighth most common cause of death from cancer in women. Recurrent EOC refers to individuals who reach complete remission following initial treatment and are therefore free of the cancer, but then experience a return of cancer cells.
The five year survival rate for EOC patients in the United States is 45%, mainly due to the cancer’s high rate of recurrence.
The growth-inhibiting mechanisms by which vitamin D helps stop tumor progression, as well as the other anti-cancer effects of vitamin D, are continuously being researched. Experimental studies have shown that activated vitamin D promotes cell differentiation and reduces the invasive potential of cancer cells in patients with metastasis.
Sunlight is the main source of vitamin D in humans, and vitamin D status is strongly correlated to seasonal variation and sunlight exposure.
Several studies have reported that prognosis of many cancers, such as lung, prostate, breast, and colon cancer is related to the season of diagnosis. For example, breast and colon cancer patients diagnosed in the summer and fall have higher survival rates compared to patients diagnosed in the winter.
It is not known whether the season of diagnosis is associated with the survival rate of patients with EOC. Indeed, studies examining the relationship between EOC prognosis and season have found conflicting results.
Additionally, no study has looked at the relationship between EOC prognosis and season of recurrence.
Researchers from China recently explored this area by looking at past data on EOC patients.
They retrieved information on 161 patients who were diagnosed with EOC at Tianjin Medical University Cancer Institute and Hospital in China from January 2005 to August 2010 and followed up until August 2013. Data on overall survival (OS), progression-free survival (PFS), season of recurrence, and season of diagnosis was collected.
OS was defined as the time from the date of diagnosis of EOC until the date of death or follow up. PFS was defined as the time from the date of diagnosis of EOC to the date of tumor progression or death.
The researchers were interested in how season of recurrence or season of diagnosis related to OS and PFS among these patients. Because vitamin D levels are lower in the winter months, a lower survival rate in individuals with recurrence during winter suggests that low vitamin D levels may play a role in the recurrence.
Here is what the researchers found when they analyzed the data:
- Of the 161 patients, 87 patients developed recurrent EOC during the follow-up duration.
- Season of diagnosis was not significantly associated with EOS survival rates.
- The median OS of patients whose cancer came back between December and March was 19.3 months, compared to 46.7 months for patients whose cancer came back between April and November (p<0.001).
- The PFS of EOC patients with recurrent diagnosis occurring between January and March was significantly less than the PFS of EOC patients with recurrent diagnosis occurring between April and November (8.2 months vs. 20.3 months, p=0.003).
“The diagnosed season for epithelial ovarian cancer was not significantly related to the prognosis of epithelial ovarian patients. The recurrent season observed in this study was associated with the survival of operable epithelial ovarian cancer patients.
They went on to add,
“In order to unveil the mechanisms and assess the relationship between season and ovarian cancer further studies about vitamin D, exposure of sunlight and diagnosed/recurrent seasons of ovarian cancer are of great interest and deserves further investigation.”
It is important to note that the researchers chose the cut-off points for the months of the groups they compared. However, these cut-offs were chosen so that they aligned with the seasons as close as possible.
There may be other variables that vary with the seasons that the researchers did not control for, and which may be responsible for, or have affected, the results seen in this study. Of course, due the observational design, no definitive statements of causality can be made.
These results suggest that sunlight may affect the course of EOC, as patients whose cancer returned during the winter months, when vitamin D levels are at their lowest, had the lowest PFS rates. An explanation for these results is that when this type of cancer recurs during times of vitamin D depletion, it gains a foothold and becomes more virulent.
Larger studies in different populations that monitor participants’ vitamin D levels before diagnosis are needed to build upon the results of this study. This will help determine if vitamin D is a factor in the relationship between season of diagnosis and recurrence and EOC survival rates.