Introduction
A « collision tumor » (CT) is a rare phenomenon defined by the proximity of two different
tumor cells during a histopathological analysis. As our study is focused on the CT in the lymph
nodes, we considered only cancers that usually have an excision of a lymph node during the
staging or the treatment of the tumor.
There are few studies about the CT and almost exclusively case reports found in the literature.
Therefore, its frequency and the prognostic of the patients with CT is not well known. The
treatment of patients with CT have not been extensively studied either, but in the literature,
there appears to be a tendency to treat initially the cancer with the worse prognostic and have
a regular follow-up of the two malignancies. The aim of our study is to evaluate the incidence,
the treatment and the prognostic of this phenomenon in the CHUV over 10 years.
Method
This is a retrospective study which was conducted on patients who had been diagnosed with
a breast cancer, a colorectal cancer, a lung cancer or a melanoma in the CHUV between 2005
and 2015 and have been diagnosed with a lymphoproliferative disease before, or at the same
time. Our inclusion and exclusion criteria matched for 28 patients: a diagnostic of a
lymphoproliferative disease before or at the same time of the second cancer, an excision of a
lymph node, the evidence of the report of the anatomopathological analyze in the medical
file. Due to the limited number of patients with CT, we chose to conduct a qualitative analysis.
Results
Four patients over the 28 included presented a CT in a lymph node. They were 61, 65, 80 and
84 years-old when they developed the CT. Two of them had an immunodeficiency. The median
time between the lymphoproliferative disease and the second cancer was 192 months (2-
240). Three patients had an association of melanoma and chronic lymphocytic leukemia (CLL).
The last one had an association of lung cancer and CLL that has been discovered because of a
reevaluation of the histological section. All of the patients have been presented at a
multidisciplinary meeting to discuss the appropriate treatment. Two of the 4 patients had an
adjuvant treatment. The median time of the follow-up was 18 months (12-24) during which
the 4 patients had a progression or a relapse of one of their malignancies. For this reason, the
treatment has been changed for 3 patients. None of the patients died during the follow-up.
Conclusion
Our study, whilst based on a limited number of cases, shows that the risk of developing a CT
might increase when a CLL is associated with a melanoma and when a patient has an
immunodeficiency. The rare phenomenon such as CT can be underestimated because of the
lack of notion of the lymphoproliferative disease in many histopathological reports, leading to
missing a diagnostic of other pathological cells by the expert. As reported in the literature, the
treatment was initially directed at the tumor with the worse prognostic for all the patients
with CT. It had to be changed for 3 patients because of the progression or relapse of the other
cancer which shows the importance of a good follow-up. In our study, the prognostic of
patients with CT (all having had a progression or a relapse of one of their tumor during the
two years of follow-up) is worse than the patient without a CT.