The Big C has never really been a show about cancer, but rather one whose story takes place in the context of the disease. After all, Cathy (Laura Linney) was already aware of her stage-IV melanoma at the start of the show's pilot, flirtatiously cracking jokes about her condition with her doctor in the opening scenes of the episode. Cancer has always taken a backseat to Cathy's rebellious and self-empowering antics, and in the show's third season, it's stuffed in the trunk, inconvenient but necessary baggage that Cathy, no longer feeling mortal after clinical trials continue to obliterate her tumors with ridiculously minimal side effects, wishes she could ditch. You get the impression that the writers probably wish they could do the same.
The success of Cathy's experimental treatment prompts her doctor (Alan Alda) to change the period at the end of her death sentence to an ellipsis, freeing the show's writers from some of the constraints of having a protagonist that was due to expire in a matter of months. But by flippantly reducing Cathy's cancer to what's essentially a footnote, the writers pass on the tantalizing opportunity to explore the ethics of the Jamisons' subsequent decision to adopt a child. Doing so knowing that you'll likely be dead before the kid loses her first tooth raises questions about responsibility and selfishness, and in the case of Cathy, it raises them for someone who, for the last two seasons, has felt a responsibility to herself to be selfish. However, with her prognosis so heavily downplayed by the show, no one—the characters, the writers, nor the audience—believes that Cathy is actually going to die anytime soon, voiding the issue, causing The Big C to miss out on a potentially captivating moral dilemma.
With this season's allotment of episodes at a premium (10, down from the previous seasons' 13), it's a shame The Big C doesn't make the most of each one of them. Cathy, her brother Sean (John Benjamin Hickey), and Andrea (Gabourey Sidibe) all spend the beginning of the season on inconsequential subplots that fail to engage. Eventually, those stories are shoved aside in favor of arcs that, while not particularly challenging or enlightening, do manage to be more compelling thanks to guest performances from Susan Sarandon, Allison Janney, and Victor Garber. The series may no longer create the types of unique points of tension and humor it did in the first season, as when Andrea and Adam (Gabriel Basso) developed a sibling relationship with sexual undertones, but its broader comedy benefits from the energy these guest stars bring to each episode.
Since the beginning of the series, creator Darlene Hunt and her writers have accommodated for the possibility of a longer run, specifically by keeping Cathy's diagnosis open-ended and choosing to have each season span only a few months. (Technically, it hasn't even been a year since Cathy was diagnosed, but tell that to Basso's growth spurt.) Cathy's shrinking tumors signify the lessening importance of cancer to the show's future: The longer Cathy lives, the longer The Big C does.