DISCUSSION :
Primary tumors of the sternum are rare, accounting less than 1% of all
primary bone tumors[3]. Ala-Kulju and
al. reported only 6 cases of primary sternal tumor in 20 years
[4].Most of these tumors are malignant
and the incidence of metastatic lesions, mainly from thyroid, kidney,
lung, breast or prostate gland cancers, is equal to primary ones
[4]. Despite of predominance of
chondrosarcomas, other tumor may be presented as a bone mass, like
lymphomas. Primary bone lymphoma (PBL) are infrequent and represents
5-7% of primary bone tumors, and 4-5% of extra-nodal non-Hodgkin
lymphomas (NHLs)[1,
2]. Extremities are the most common
sites of PBL (femur 27%, pelvis 15%, tibia and fibula 13%), and so
sternal localization is very rare[1].
The absence of specific signs of sternal lymphomas makes the diagnostic
difficult. In fact, clinical signs are usually a firm sternal painful
swelling, progressing since several
weeks[3]. General symptoms like night
sweating and loss of weight can be
absent[1]. Radiological explorations
often show a lytic mass with effraction of the bonny
cortex[5]. Extension can be found to
both deep and superficial layers and lymph node involvement is less
frequent in bone non-Hodgkin lymphomas
[5]. The local extension is better
explored by an MRI than by a scanner
[6], and comparing to the rest of
radiological tools, Positron Emission Tomography coupled with computed
tomography is more sensible in the assessment of extension, especially
in multifocal forms, and helps in the follow up after
treatment[1]. All these elements
explain why the diagnostic represent a challenge on itself.
Taking into consideration the frequency of malignant nature of sternal
tumors, a histopathological confirmation is often necessary before any
treatment, especially that in some cases, sternal resection with a
curative oncological intent may be large with a complex
reparation[2]. Needle biopsy is
considered as insufficient to make the diagnosis, and a surgical biopsy
is often needed[4]. In our case, and
because of the special conditions with the COVID-19 epidemic and the
rapid progression of the mass, we did not perform a surgical biopsy, and
we erroneously considered the sternal mass as a chondrosarcoma. Indeed,
there is no radiological signs that are specific to a particular type of
tumor. Furthermore, malignant degeneration of untreated benign tumors
was reported, justifying an aggressive approach in some doubtful
cases[3]. In the case reported by
Faries and al, surgical resection was maintained even after an open
biopsy with frozen examination in an antalgic intent and to reduce the
size of the tumoral process [5].
The diagnostic of DLBCL is based on histological examination with
immunohistochemical testing. Referred to World Health Organization
Classification of Soft Tissue and Bone Tumours, the group of a single
skeletal site with or without regional lymph node involvement is
considered primary lymphoma of bone. Expression of CD20 represents a
therapeutic target. Indeed, anthracycline-containing chemotherapy
coupled to Rituximab is considered currently as the first line treatment
of CD20-positive DLBCLs [1].
Radiotherapy at a dose of 30 Gy may be indicated after chemotherapy for
the treatment of non-Hodgkin lymphomas including extra-nodal sites, as
it was revealed on a British randomized trial. Higher doses may be
reserved in cases of suboptimal response to chemotherapy
[1]. Surgical resection, actually, do
not have a place in the treatment of DLBCLs instead of surgical biopsy.
Conclusion : The diagnosis and treatment of sternal tumors
may represent a real challenge. Even if chondrosarcomas are the most
common, rare tumors such as DLBCLs must be kept in mind, especially that
treatment strategies are different.