En este caso "primitivo de" significa que el tumor primario está localizado en el testículo.
Se puede decir también: Primary non-Hodgkin's lymphoma of the testis.

Primary testicular non-Hodgkin's lymphoma was first described as a clinical entity in 1866. It is a rare disease and accounts for 1% of all non-Hodgkin's ...
www.popline.org/docs/1783/324123.html

Primary testicular non-Hodgkin's lymphoma with atrial mass as an initial presentation of acquired immunodeficiency syndrome. Halloush RA, Arabi H, ...
www.ncbi.nlm.nih.gov/pubmed/17676218

Bilateral primary non-hodgkin's lymphoma of the testis. Liamj Hurley Corresponding Author Contact Information , Charles R. Burke, Santos K. Shetty, ...
linkinghub.elsevier.com/retrieve/pii/S0090429599805044

As an example of the original word in English translated as "primitivo" in Spanish:

[Primary non-Hodgkin's lymphoma of the prostate gland]

(Linfoma no-Hodgkin primitivo de glándula prostática.)
Full Abstract
The clinical, morphological, microscopic, immunohistochemical, and ultrastructural findings in a case of primary non-Hodgkin's malignant lymphoma of the prostate gland is reported.
www.find-health-articles.com/rec_pub_2619341-primary-non-ho...