My suggestion:
The limits of exeresis locally pass into the lesion area.

I believe what they mean is that there is a risk in this situation. In oncological surgery practice, the limits of exeresis should not normally touch the lesion area, otherwise local recurrence is more likely. Here, however, the limits of exeresis seem to be encroaching upon the lesion area, in a localized fashion.

1. Explanations of the risk:
http://documents.irevues.inist.fr/bitstream/handle/2042/3872...
l’atteinte des limites d’exérèse lors d’une chirurgie conservatrice augmente le risque de récidive locale

http://www.chirurgie-viscerale.org/main/formationcontinue/mi...
Sur le plan histologique, s'il existe du carcinome ductal in situ de bordure, [...]l'exérèse doit passer à distance > 5 mm. [...] Si la résection passe en limite ou en contact avec la tumeur invasive, on doit réintervenir.

2. Explanation of 'limits of exeresis':
Not quite the same as 'boundaries of the excision.' A surgeon can determine or evaluate the limits of exeresis before actually performing an excision.
Or, by determining the limits of exeresis, the surgeon can gain more accuracy in identifying the location of a decayed lesion:

http://www.acteongroup.co.uk/products/digital-imaging/digita...


3. By 'focalement' I think they simply mean 'locally, in a localized fashion':

http://medical-dictionary.thefreedictionary.com/focally
Relating to a localized area.

I am posting this alternative because I think the use of the term "extends" is inappropriate in this context.
The scenario is of course not that the tumour is spreading but that the surgeon has cut through it !
An EN report would usually say something like: "tumour present at excision margins in places"